ndow -Glass 
1 the Making 


William L.Monro  _ 


American Window Glass Company 
Pittsburgh, Pa. U.S.A. 


Window Glass 
In the Making 


Window Glass 


in the Making 


An Art, A Craft, A Business 


BY WILLIAM L. MONRO 
President and General Manager 
American Window Glass Company _ 


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American Window Glass Company 
PITTSBURGH 
1926 


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ForREWoRD 


Definition of Window Glass 


CHAPTER 
CHAPTER 
CHAPTER 
CHAPTER 
CHAPTER 
CHAPTER 
CHAPTER 
CHAPTER 
CHAPTER 
CHAPTER 


CHAPTER 


CHAPTER 
CHAPTER 
CHAPTER 
CHAPTER 


CHAPTER 


Appendix—U. S. Govt. Master Specifications 


I 


TE 


III 


IV 


XV 


XVI 


CONTENTS 


Uses 

Quality 

Glass—Its Origin 
Composition 
Melting and Refining 
Ladling and Blowing 
Flattening 
Annealing 

Cutting and Sorting 


Boxes and Packing 


Labels, Quality Slips, and 
Branding 


Warehousing and Shipping 
Defects in Glass 

Window Glass Wave - 

Our Productions 


Comparison of Glass 


with Comments 


Index 


107 


} 


FOREWORD 


F the world were deprived of window 
& glass today, civilization would beturned 
ie @ back at least 500 years. Without it we 
% would be compelled to forego many of 
the conveniences, comforts, and luxuries of modern 
life and would revert to the inconveniences, the 
discomforts, and the hardships of medieval times. 

No matter where we go or what we do, we are 
confronted by the ever-increasing uses of window 
glass. In fact, it is in such general use that probably 
none of us, except those closely allied with the pro- 
duction of window glass, has any appreciation of its 
importance or realizes how essential it is, and has 
been, to the progress of mankind. 

It is the purpose of this book to tell enough about 
window glass to give architects, dealers, contrac- 
tors, home-builders, and all other users a better 
understanding of its nature and characteristics, in 
otder to render them more competent to judge the 
quality. With this knowledge they will demand 
“The Best Glass’’ obtainable and will refuse to ac- 
cept glass of inferior quality, especially when pay- 
ing for the better article. This knowledge is not 
only of interest but of great value to every user of 


window glass. 


10 Window Glass in the Making 


Such information has not been available hereto- 
fore in books or other publications, for there is 
practically no literature on the subject of window 
glass. 

During years of study and experimental work in 
the development of a new process of manufacturing 
window glass, and by the expenditure of millions 
of doJlars in bringing that process to complete 
commercial success, we acquired a comprehensive 
understanding of it that could not be gained in any 
other manner. 

Yet we realize that there is much we do not know 
about it. In that respect we differ from what the 
renowned, and probably the most learned man of 
his time, Professor Jowett, of Baliol College, was 
reported to have said, ‘‘All that known is, I know 
it; what I know not is not knowledge.” ; 

To acquaint the reader with much of the knowl- 
edge that we have acquired, it is our intention to 
define window glass; to point out the variety of its 
uses in order to show how they are affected by the 
quality; and to explain what is meant by the term, 
‘“quality.’’ This will be followed by an account of ~ 
the origin of glass for its bearing on the compo- 
sition. 

We shall then describe briefly our process of man- 
ufacturing window glass, by tracing the raw ma- 
terials of which it is made through the different 


Window Glass in the Making 11 


steps of the process until they finally appear in the 
form of flat sheets of clear glass, ready for use. 

However, it is not the intention to go into a 
technical description of the process of manufacture, 
such as will interest only the trained chemist or 
the glass engineer, but to describe it in such a man- 
ner as will interest those who desire to add to their 
fund of useful information, and those who have not 
the time to give to a highly technical exposition of 
the subject. 

For the benefit of those who desire a more com- 
plete commercial knowledge of window glass, its 
various thicknesses and qualities, with the rules for 
grading, and the method of glazing, an Appendix is 
added, wherein is set forth an exact copy of the 
“U. S. Government Master Specification for Flat 
Glass for Glazing Purposes,”’ so far as it relates to 
window glass, with our notes and comments thereon. 

The Appendix also sets forth the fourteen reasons 
why our glass is ‘“The Best Glass.”’ 


American Window Glass Company 


DEFINITION OF WINDOW GLASS 


2) PAGS Qsvarry we think of window glass as a 
a K hard, clear, brittle substance, and do not 

( +7) ;) realize that, at a sufficiently high tem- 
Sy perature, it becomes a liquid.Whencold, 
it an great tensile strength and elasticity. Everyone 
who played marbles, when a child, had his favorite 
‘‘glassie,’’ that could be used only because of that 
elasticity. | 

Glass is a poor conductor of heat. One end of ashort 
rod of glass can be held in the bare hand without 
discomfort while the other end is being melted in a 
furnace. 

The chemists say that it is an amorphous substance 
—that is, having no regular structure; and diaphan- 
ous—that is, translucent and transparent. They go 
further; and say that it is a salt. 

No matter how it is defined or described, to con- _ 
vert ordinary sand mixed with a few other in- 
gredients into a bright, clear substance of fine qual- 
ity, which we call window glass, and which affects 
so greatly our welfare and happiness, is an art that 
requires the science of the chemist, the genius of 
the engineer, and the technique of the artist. 


CHAPTER I 


USES 


) a material that would let in the light 
M/@9 and keep out the elements, that would 
keep in the heat and shut out the cold. Its develop- 
ment has kept pace with the progress of civiliza- 
tion. From the skin tents of the Nomads to the 
solid doors and shutters in the cabins of the fron- 
tiersmen; from the rice paper and oiled parchment 
in the windows of the Orient to the dazzling bril- 
liance of the crystal palaces of the Occident, we 
trace its ever-increasing uses. 

Today it is in such general use that it has become 
known as “‘common window glass.’’ Recognizing 
this fact, Congress has used this designation in 
many of the tariff laws. 

Not always has it been such a commonplace arti- 
cle. Even as late as the fourteenth century Richard II 
issued a writ to scour the counties of Norfolk, 
Northampton, Leicester, and Lincoln, to find glass 
to repair the windows in the castle at Stamford, 
built in honor of his mother. 

In the sixteenth century, window glass was so 


The Skin Tent— 
The habitation of many 
nomadic tribes before glass 
gave permanence to civili- 
Ration. 


14 Window Glass in the Making 


expensive in Germany that the law provided that 
on the death of the owner of a building, the glass 
belonged to his executors, but the windows went to 
theheirs, ‘‘for the houseis perfect without theglass.’’ 

As late as 1686, Sir R. Worsley, writing of his 
travels, said, “‘In all ye great towns of Italy, except 
Genoa, and in this city (Murano), they have paper 
in their sashes instead of glass.’’ 

For centuries it continued to be regarded as a lux- 
ury and was taxed accordingly, down torecent times. 


_ It is aquestion whether the ‘‘window tax”’ has been 


entirely abolished in all European countries to this 
day. 

We see so much window glass and can obtain it 
so easily and so cheaply that we fail to appreciate 
its value or the effect it has on our lives. We do not 
realize how it changes the lives of those who would 
otherwise be obliged to live in shadows and dark- 
ness. Isak, the hardy frontiersman in Knut Ham- 
sun’s ‘‘Growth of the Soil,’’ found it a bright and 
wonderful day when he was able to put glass in 
the windows of his hut. He was no longer obliged 
to depend upon the firelight to enable him to work 
at his bench. 

Some idea of the extent of its use here may be 
gained from the fact that the American Window 
Glass Company has six large factories in different 
parts of this country. These have the capacity to pro- 


A residence— 
Pasadena, California 


Window Glass in the Making 15 


duce annually about three hundred million square 
feet, or six million fifty-foot boxes of window glass, 
which makes this Company “‘The World’s Largest 
Producer’’ of window glass. If all this glass were of 
single thickness, cut 24 inches square, and packed in 
fifty-foot boxes, and these boxes laid on the ground 
end to end, they would make a sort of boardwalk 
extending 2651 miles, or from the Atlantic to the 
Pacific Coast. 

Window glass has an almost endless variety of 
uses. An enormous quantity is consumed for other 
purposes than glazing; that is, putting it into win- 
dow frames. Of course, the largest amount is glazed 
in windows and doors of houses, schools, churches, 
colleges, hospitals, hotels, stores, greenhouses, fac- 
tories, in fact buildings of every kind. Considerable 
is used in street railway and railroad coaches, in car- 
riages, trucks, and automobiles. Much is used for 
other articles such as eyeglasses, photographic dry 
plates, lantern slides, microscopic slides, X-ray 
plates, vanity cases, toilet articles, pictures, mirrors, 
showcases, counters, shelving, tops for desks, tables, 
and for furniture of every description. 


WHY USE WINDOWS? 


Few people appreciate sufficiently the importance 
of windows in buildings. There should be as many 
as possible; but if limited in number, they should 


A residence— 


New York City 


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16 Window Glass in the Making 


be as large as possible. The old Gothic cathedrals 
were built with the windows as large as possible, 
and just enough stonework to support the building. 

In factories,workrooms, offices, hospitals, school 
buildings, and homes, the use of clear window glass 
to “Let in the Sunlight’’ is of compelling impor- 
tance, for with it you let in health and happiness. 
The sun’s rays are nature’s greatest purifier, which 
the medical profession has recognized by using 
“artificial sunlight’’ for disinfecting wounds, and 
. for therapeutic treatments. 

Careful and exhaustive tests have demonstrated 
that workers in a factory in which the windows are 
glazed with clear window glass do better work than 
those in factories in which obscure glass is used. 
When at the workbench, the opportunity of *‘catch- 
ing a glimpse’ of the outside world exerts a psycho- 
logical effect on the workers. It takes away the feel- 
ing of confinement and promotes cheerfulness and 
contentment. A contented workman always does 
the best work. 

For economical reasons there should be plenty of 
windows in a building. Window glass costs less per 
square foot of wall space than lumber, tile, or brick. 
At the present time, in a modest brick dwelling of 
avetage size, the window glass represents less than 
one-half of one per cent. of the total cost of the 
building. 


fat LER II 


QUALITY 


ity,’’ or how it may be determined. 

“Quality’’ in window glass covers not only the 
chemical composition and physical properties, but 
alsothe grade of the glass from the standpoint of de- 
fects. It may be of good quality so far as its composi- 
tion and properties are concerned, but of very poor 
quality as regards the defects. The differences in com- 
position and properties can only be discovered by 
analysis and test; but in grading, they can readily be 
detected by comparing different makes of glass. 

Grading is separating the lights, or panes, of glass 
into different grades or classes of quality, according 
to the character, size, number, and position of the 
defects, which affect not only the appearance of the 
glass itself but of the objects viewed through it. 
The casual observer notices these defects, but thinks 
they are inherent in the process of manufacture, and 
therefore unavoidable. He does not know that they 
are unnecessary, and that window glass which is 


17 


18 Window Glass in the Making 


practically free from them may readily be obtained. 

A beautiful house showing the care, thought, and 
artistic sense of the architect who planned it, is 
often disfigured by the poor quality of the glass he 
unwittingly permits to be placed in the windows. 
The enjoyment of one’s home is sometimes spoiled 
by defects in the glass that hinder the vision. Fre- 
quently the appearance of a fine picture is ruined by 
the execrable quality of the glass used in the frame. 
The pleasure of a ride through an interesting part of 
- the country in a railway coach, street car, or an auto- 
mobile often is taken away by the poor quality of 
the glass through which one is obliged to view the 
scenery. Glass of poor quality not only spoils the 
view, but offends the eye, and irritates the nerves of 
one compelled to view continually objects distorted 
in appearance by its defects. 

A very large amount of window glass produced is 
of such poor quality that it is not fit for commercial 
use and is really rubbish which should be remelted. 
Instead of disposing of it in this manner the inca- 
pable manufacturers who produce this glass putiton 
the market at low prices. Notwithstanding its poor 
quality, such glass is finally used for many purposes 
for which it is grossly unfit. This would not be pos- 
sible if more were known about it. 


Window Glass in the Making 19 


' THE BEST GLASS”’ 


The American Window Glass Company produces 
a very large quantity of a highly perfected product 
of beautiful lustre, graded to the highest possible 
standard and known as ‘‘The Best Glass.’’ It is suit- 
able for every purpose. Its production is possible 
only with a process conducted on scientific prin- 
ciples, by a Company that has built up, after years 
of effort, an organization of highly skilled employ- 
ees, who pride themselves on their workmanship as 
greatly as the Company prides itself on its product. 
Every user can obtain ““The Best Glass’’ if he in- 
sists upon having the American Window Glass 
Company’s brand and is competent to judge the 
quality of the glass furnished. The price of it is not 
substantially different from that of glass of inferior 
quality. 


CHAP Tite 


GLASS—ITS ORIGIN 


/ RHE origin of glass is still in doubt. Many 
ee howe theories have been advanced by ancient 
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§ and modern writers to explain its dis- 


the Egyptians discovered glass; others claim it was 
a discovery of the Chinese. Probably the most accu- 
rate account of its origin, and certainly a very plaus- 
ible one is that related by C. Pliny the Second in his 
“History of the World,’’ Volume 36, Chapter 27. 
According to Pliny, there was in Phoenicia a short 
river, called Belus, that flowed from Lake Candeboea 
to the sea. Its waters were muddy and unwholesome, 
and nothing was to be found on its banks but sand. 
This had been cast up by the sea, and from frequent 
washings by the waves was pure and white and suit- 
able for making glass. 

One day some traders, who had been gathering a 
cargo of nitre, sought, along the banks of the river, 
stones on which to mount a tripod to cook their 
food. Not finding any, they were obliged to use 
blocks of nitre taken from their cargo. Under the 
heat of the fire, the sand coming into contact with 


Illustrating the discovery 
of glass as related by Pliny 
_ the Second 


Window Glass in the Making 21 


the nitre, which acted as a flux, formed a vitreous 
substance— ‘glass. 

Though there is room to doubt that this is the 
true account of the origin of glass, there are certain 
basic features in it that make it appear not only 
plausible but easily possible. From our later know!l- 
edge, we know that sand alone may be fused intoa 
vitreous mass by applying a very high degree of 
heat; and that by mixing with it a quantity of soda, 
the temperature required to do this is greatly les- 
sened. By using nitre, which contains a large per- 
centage of soda, these ancient traders used an ingre- 
dient that materially lowered the melting point of 
the sand and made possible its reduction into glass. 

To demonstrate the possibility of the discovery of 
glass in some such manner, we recently caused a 
wood fire to be made in the open air. Small logs 
were laid on a bed of glass sand mixed with an 
equal quantity of carbonate of soda. In order to se- 
cure accurate information of the degree of heat that 
could be obtained from such a fire, a standard pyrom- 
eter couple was inserted into the bed, and frequent 
readings taken. The fire was kept burning about two 
hours. The highest reading, 2210 degrees Fahren- 
heit, was obtained when the fire had been reduced 
to a mass of burning charcoal. After the fire had 
completely burned itself out, the wood ashes were 
removed and a portion of the bed was found to be 


i 


Residence— 
Brookline, Mass. 


22 Window Glass in the Making 


fused into a vitreous mass—the same kind of glass 
discovered by the Phoenicians. In a similar demon- 
stration, with a bed of glass sand mixed with an 
equal quantity of nitre, a like result was obtained; 
but when a bed of glass sand unmixed with any 
other ingredients was used and subjected to the same 
kind of a fire, there was not the slightest trace of 
any fusing of the sand. 

It seems quite plausible, therefore, that glass was 
first made somewhere along the shore of the Sea. 
Many centuries after Pliny, it was found that when 
seaweed was burned, its residuum, called ‘then = 
contained a large amount of carbonate of soda. Sub- 
sequently this was used in making glass, and there 
became known to the trade the term, “kelp glass.”’ 

It requires no great stretch of the imagination to 
think that at some time there had been kindled 
along a sandy shore a great bonfire of dry seaweed, 
with perhaps a lot of driftwood, which left amid 
its charred embers the vitreous mass we now call 
glass. 

Owing to the impurity of the raw materials and 
to the cruder methods of manufacture, the glass 
made by the ancients was not the bright, clear, 
transparent article in use today, but was much dark- 
er and contained many bubbles and foreign parti- 
cles, which made it more translucent than trans- 
parent. Saint Paul refers to this feature when he 


A Virginia 
Plantation House 


Window Glass in the Making 23 


says, ‘For now we see through a glass, darkly’’— 
I Cor., xiii, 12. 

Centuries elapsed before this discovery by the 
Phoenicians was put to any practical use. In fact, 
we may say that glass really had to be rediscovered 
before glass articles of any kind could be produced. 
While it is not the intention to go into the history 
of glass making, the story of its origin is recounted 
for the bearing it has on the development of the 
various compositions subsequently used in making 
window glass. — 


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COMPOSITION 


the ingredients na their proportions spread to 
others, who put it to practical use; but all of these 
early manufacturers guarded with care the secret of 
their formulas. This is proven by the evident lack 
of exact information shown by the old writers from 
the time of Agricola, A. D. 1556. This secrecy has 
been maintained by glassmakers down through the 
centuries and continues to a considerable extent to 
the present time. Today, very few will disclose the 
exact proportions of the materials used in making 
their glass. They believe that the slight variations 
they make from time to time in the composition 
ate responsible for producing glass superior in qual- 
ity to that of their competitors. They seem to be 
blissfully ignorant of the fact that the chemist of 
today, by analyzing a small sample of their glass, 
can quickly solve their closely guarded secret. 
Today, window glass is made from silica (sand) 
mixed either with sulphate of soda (salt cake) or 


oe 


26 Window Glass in the Making 


carbonate of soda (soda ash), or with a combina-. 
tion of these two forms of soda. To these ingredients 
is added lime, either in the form of ground lime- 
stone, burnt lime, or dolomite. With sulphate of 
soda, a small amount of carbon is added, either in 
the form of crushed coal or coke, or ground char- 
coal. Sometimes arsenic, manganese, or other de- 
colorizers, in small quantities, are introduced into 
the mixture, whenever it is desired to obtain glass 
free from the usual greenish tint which is caused 
by a small percentage of iron in the materials or in 
the clay of the pots or blocks of the furnace. 

Upon the purity of the materials, their degree of 
fineness, and the proportion in which they are used, 
depend the color, quality, toughness or brittleness, 
and density of the glass produced. 

The American Window Glass Company uses the 
purest materials obtainable, ground to the requi- 
site degree of fineness. They are mixed in certain 
proportions, determined after years of study and ex- 
periment, and produce “‘The Best Glass’’ possible, 
as is shown by every chemical and physical test 
to which it can be subjected. 

The table on the next page represents about an 
average analysis of the window glass produced by 
the American Window Glass Company. 

Window glass of approximately this analysis, 
made by our process, will have greater tensile 


Old House at 


Germantown, Pa. 


Window Glass in the Making 27 


strength, a higher modulus of rupture, and more 
resistance to the action of moisture than glass hav- 
ing a lower percentage of silica or lime, or a higher 
percentage of soda: 


Silica 73.25% 
Lime 12.50 
Soda 12.50 
Alumina Aa i 
Other Ingredients 1.00 
Total 100.00 


An analysis of pieces of glass from windows found 
in the ruins of Pompeii, which was destroyed in 
79 A. D., gave the following result: 


Silica 69.45% 
Lime 7.24 
Soda 17.51 
Alumina 55> 
Other Ingredients 22 
Total 100.00 


It is interesting to know that the composition of 
French window glass that was being produced at 
the date of that analysis, about 1855, was almost 
identical with that of the Pompeiian glass. Such 
glass was of very poor quality from the standpoint 
of strength and resistance to discoloration or “‘fade.”’ 


Windows 


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28 Window Glass in the Making 


COMPOSITION OF GLASS MADE BY 
OTHER PROCESSES 


At the present time many factories using some of 
the other new processes of making window glass 
require molten glass that can be worked at com- 
paratively low temperatures without devitrifica- 
tion. Devitrification, as its name indicates, is the 
changing of the glass from a liquid condition into a 
white, opaque solid that does not have the charac- 
teristics of glass. It is usually caused by maintain- 
ing the molten glass at too low a temperature, 
which varies according to the composition of the 
glass. It begins with the formation of very small 
crystal-like particles resembling large grains of very 
white sand or small stones, which cause enormous 
breakage during the process of manufacture. These 
gradually become larger and more numerous, until 
they finally permeate the entire body of glass and 
change it into a hard white substance resembling 
porcelain. This is often called ““The Porcelain of 
Réaumur,”’ after the celebrated French physicist 
who first made a study of this change in the glass. 
It is interesting to know that if this devitrified mass 
is subjected to a sufficiently high heat, it will again 
become liquid glass. 

In our process of manufacture, the glass is worked 
at such a high temperature thatit doesnot devitrify. 


Window Glass in the Making 29 


This enables us to use a composition that produces 

glass with the best physical and chemical properties. 
To obtain glass that will not readily devitrify at 

the low temperatures required for those other proc- 

esses, very important changes are made in the com- 

position, which produce a quality of glass inferior 

to ours from the chemical and physical standpoints. 
The changes are as follows: 


1. The percentage of silica is lowered. Therefore 
less heat is required to melt the composition, but 
the resultant glass does not have the strength or 
durability of window glass containing a higher 
percentage of silica. 


2. The percentage of soda is increased. This en- 
ables the composition to be melted at a lower 
temperature, but makes the glass less dense and 
more hygroscopic; that is, causes it to sweat more 
readily. 


3. The percentage of lime is lowered. Reducing 
the amount of lime in the composition causes the 
glass to set, or harden, more slowly and thereby 
lowers the temperature at which it can be worked 
without devitrifying. This reduction, however, 
causes the glass to have less ductility and less 
body, and increases the tendency of the soda in 
the glass to attract the humidity of the air; or, in 
other words, renders it more deliquescent. 


30 «© Window Glass in the Making 


As a result of these changes in the composition, the 
glass produced by those processes analyzes about-as 
follows: | 


Silica 72.00% 
Lime 10.75 
Soda 15.50 
Alumina 75 
Other Ingredients 1.00 
Total 100.00 


Glass of the foregoing analysis does not have the 
same strength or durability as glass that contains 
the correct proportions of the different ingredients, 
and it is much more susceptible to attack by mois- 
ture. It will therefore lose its brilliance of surface 
more quickly by discoloring, z.e., fading, staining, or 
rusting. 


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fot ER V 


MELTING AND REFINING 


@)\(@) fit the raw materials thoroughly mixed 
a (2y/) in suitable proportions, then comes the 
melting. Formerly this was done in 
J furnaces built to contain large clay 
pots in which the composition was melted. In mak- 
ing window glass this system has been entirely 
superseded in this country by the continuous melt- 
ing regenerative tank system, which uses either 
producer gas or natural gas for fuel. 

The American Window Glass Company has thir- 
teen continuous glass melting tanks, or furnaces, of 
the most modern construction, five of which are 
much larger than any other glass melting furnaces 
in the world. The largest ones are 30 feet wide, 140 
feet long, and 5 feet deep. To visualize a tank of 
such size, picture an enormous swimming pool with 
a capacity of 172,627 gallons, filled with 1800 tons 
of molten glass, varying in temperature from 2200 
to 2700 degrees Fahrenheit. If all the glass in one of 
these large furnaces were made into a light or pane 
of single strength thickness one foot wide, it would 
extend for a distance of six hundred miles, or from 
Pittsburgh to St. Louis. 


31 


CHARGING THE FURNACE 


Testing Laboratory constantly 
checking purity of materials 


Window Glass inthe Making 33 


In the modern continuous melting tank system, 
the raw materials are placed in the furnace along 
with some broken glass called, ‘‘cullet,’’ which facil- 
itates the melting. Then they are exposed to the 
heat of the furnace in the melting zone until they 
ate entirely reduced to a viscous mass, full of bub- 
bles formed by the gases given off during the melt- 
ing, which have not yet been able to escape during 
that process. Additional raw materials are fed into 
the furnace at regular intervals as rapidly as the 
preceding charges are melted. The furnace is main- 
tained at the melting temperature continuously for 
months, and there is no cessation of the melting, the 
taw materials being fed in at one end, while the 
molten glass is taken out at the other end, except 
during the usual Sunday shutdown. This continues 
until the furnace has been burned out to such an ex- 
tent as to need repairs. 

The melted viscous mass of glass moves slowly 
down the furnace, passing through a hotter zone, 
which renders the mass still more liquid, and thus 
allows the pent-up gases to escape. This is the re- 
fining process. If the temperature of the refining 
zone is not high enough, or if the glass passes 
through it too quickly, the glass will not be prop- 
etly refined and will contain bubbles of various 
sizes, some quite large, and some as small as a pin 
point. 


POURING MOLTEN GLASS 


(The last ee preceding the drawing 
or blowing process) 


Bd Ladle Bosh which cools 
the ladle after the fe 


process 


Window Glass inthe Making 35 


The refined glass continues on its way through 
the furnace to the working zone, gradually cooling 
as it gets farther away from the fire of the furnace. 
By the time it has reached that zone, it should be 
sufficiently cooled to permit the necessary handling 
by the workmen. Unless the furnace is properly con- 
structed, it is impossible to secure the even grada- 
tions of temperatures necessary to obtain glass of 
suitable working consistency. Our furnaces have 
demonstrated their efficiency in this respect by pro- 
ducing more glass of good quality than any other 
window glass furnaces of which we have any 


knowledge. 


linders into 


ing cy 
short lengths 


S 
S 


BLOWING AND DRAWING THE CYLINDERS 


GBA PTER VI 


~LADLING AND BLOWING 


] rmRODAY, window glass is either blown in 
Gy i wy the old-fashioned way by hand and lung 
( ; iQ power, a method that is fast dying out, 
(54 KO) or is drawn in sheet form from a fore- 
hearth attached to a tank furnace, or is made by 
the American Window Glass Company’s method of 
drawing and blowing it mechanically in the form 
of large cylinders, a process invented by John 
Lubbers. 

In our process, by means of a ladle that holds 
enough glass to make one large cylinder, or as much 
as would fill a good-sized bass drum, the molten 
glass is ladled from the huge melting furnace into a 
comparatively small pot located in a fixed position 
beneath the drawing and blowing machine. This 
pot is reversible; that is, with a working cavity on 
each side, and is mounted in a small furnace, or 
heated drawing kiln. Each of our very large tanks 
has twelve of these drawing kilns, and each of the 
smaller ones has eight. 

As soon as the upper cavity of the pot is filled with 
molten glass, the operator lowers into the glass a 


37 


COMPLETED CYLINDER 


(Cylinders in foreground being cut into 
short lengths) 


Carrying glass before splitting 


Window Glass inthe Making 39 


hollow stem blow pipe, with a mushroom-shaped 
head. This blowpipe is hung on a cage that travels 
vertically between a pair of guides erected above 
the pot and is connected to a telescoping air sup- 
ply pipe. A motor driven fan supplies the air pres- 
sure. The blowpipe, having taken hold of the glass, 
is then slowly elevated by the machine, which, at 
the same time, introduces at the glass level a small 
quantity of air. As the blowpipe is elevated, the 
amount of air is gradually increased, and the plastic 
glass is uniformly and gradually distended in a 
swelling curve like the neck of a bottle, until it at- 
tains the diameter desired for the cylinder. The 
machine then continues to elevate the blowpipe 
and automatically furnishes the amount of air 
needed to keep the cylinder distended to a uniform 
diameter until it reaches the limit of the length of 
its draw. 

When the cylinder is completed, the lower end 
is severed from the glass in the pot; and by 
another mechanical device it is quickly lowered 
into a horizontal position and placed on a “‘horse,’’ 
a receptacle especially designed to receive it. As 
soon as one cylinder is completed, the potisreversed, 
and the other side of the pot is turned up into the 
drawing position, ready to receive a ladle of glass 
for the next cylinder. During the drawing of one 


Ay 


wv 


Window Glass inthe Making 41 


‘cylinder, the fire in the kiln melts out the cold 
glass remaining in the under side of the pot after 
the drawing of the preceding cylinder and prepares 
‘it to receive the glass for another cylinder. This 
renders the operation practically continuous. 

Like mushrooms, these huge cylinders grow from 
the molten glass in the pots, rising slowly and silent- 
ly, impelled as if by an unseen power, to a great 
height, until their tops almost disappear in the 
shadows of the building structure. When finished 
they resemble enormous bottles. Some idea may be 
gained of their size when you consider that if one 
of them were filled with milk it would hold 6804 
quarts, or about seven tons. 

They are made in various lengths, diameters, and 
thicknesses. The diameters are regulated by the air 
pressure introduced into the cylinder, and average 
about 30 inches in commercial operation, although 
we have made them 48 inches. The diameter of the 
pots from which they are drawn, of course, limits 
the diameter of the cylinders that can be made. 
Their length is limited by the height of the struc- 
ture on which the machines are placed, and by the 
amount of glass the pots will hold. The cylinders 
usually are about 48 feet in length from blowpipe 
to “‘hole end.’’ The thickness is regulated by the 
speed of draw, and varies from 1/39 to %A¢ of an inch 
in thickness. 


Windows along 
@ street in Wales 


42 Window Glass in the Making 


ADVANTAGE OF OUR BLOWING PROCESS 

Our mechanical process of drawing and blowing 
the cylinders imparts to the glass a preliminary 
annealing, and so affects the physical structure of 
the glass as to render it stronger and tougher than 
window glass made by any other process. It in- 
sures a uniformity of thickness in the glass, far 
superior to that produced by the hand blowing 
method, and equal in every way to that made by 
any other process. 


CAPPING 
After the large cylinder has been laid on the 
horse, the upper part, or cap, and any uneven por- 
tion of the “‘hole-end,’’ are removed, and the re- 
mainder of the cylinder is cut up into sections of 
the desired length by means of electrically heated 
wires. This process is known as “‘Capping.”’ 


SPLITTING 

The sections of the large cylinders are prepared 
for the next stage of the process (the flattening) by 
cutting them lengthwise into segments of the re- 
quired sizes, either by means of an electrically 
heated iron, or wire, or by a diamond splitting tool. 
This is known as ‘‘Splitting,’’ or ‘“Cracking-open.”’ 
When the cylinders are made of small diameter, the 
sections usually are only split once lengthwise, and 
are not cut into segments. 


Llivia in 
the Pyrenees 


Pear rIER Viti 


FLATTENING 


RHE ‘‘cracked-open’’ sections of the long 

a me cylinders of small diameter, and the 

Ae () segments of the cylinders of large di- 

Og Lay) By ameter are now ready for the next steps 
in 1 the process—the flattening and the annealing. 

For this purpose, furnaces, or ovens, of special de- 
sign are required. In this country these ovens are all 
of the same general type, but in Europe quite a dif- 
ferent type of flattening oven is used. 

Although many improvements have been made 
from time to time in various other steps of the proc- 
ess of manufacturing, practically none had been 
made in the flattening process for more than one 
hundred years, until the American Window Glass 
Company recently worked out certain changes. These 
make it possible for this Company to secure better 
results than can be obtained by any other producer 
of cylinder drawn glass. 


The flattening ovens used in America consist of a 
horizontal revolving wheel built in four segments 
and mounted in a furnace, or oven, divided into four 
compartments. On each segment of this wheel is 
placed a perfectly flat and highly polished clay 


43 


aH 


U] 
i 


wit 


2 


Ut} 


| 


! 


AMA 


THE FLATTENING PROCESS 


(A perfectly flat glass of high lustre is 
thus produced.) 


Annealing accomplished within the lebrs 
gives the glass strength and greater 
resistance to breakage 


Window Glass in the Making = 45 


|stone, known as a ‘‘flattening stone.’’ The oven, of 
|course, is heated to the required temperature, and an 
linlet canal, or “‘stick hole,’’ is provided for intro- 
|ducing the glass into the highly heated portion of 
|the oven. 

| The glass is placed on a small carriage, which is 
shoved into the heat of the oven adjacent to the 
\flattening wheel. When the glass has been heated to 
the required temperature, it is then lifted from this 
catriage and placed on the flattening stone. It is now 
sufficiently plastic to permit it to be flattened. 

If the glass has been introduced into the oven in 
the form of a segment of the cylinder, the workman 
at once uses a water-soaked and charred block of 
wood, called a flattening block, or polisher, with 
which he rubs or “‘irons’’ the surface of the glass and 
flattens itintoa sheet, whichconformstothesmooth 
surface of the flattening stone. When properly done, 
the block imparts a beautiful lustre or polish to the 
surface of the glass. 

If the glass has been introduced into the oven in 
the form of sections of cylinders of small diameters 
jthat have been split open lengthwise, the workman 
is obliged to open up the cylinder withaspecial tool, 
by spreading it along the lengthwise split or “‘crack- 
open’’ to such an extent that the edges of the split 
fall away from one another toward the sides of the 


46 Window Glass in the Making 


flattening stone. He then takes the charred bloc 
and irons, or polishes, the glass as before. | 

Much better results are secured by flattening seg 
ments of the cylinder than by flattening the entit| 
cylinder. The development by us of the forme 
method of flattening resulted in a great improve 
ment in the character of the work, in the freedo 
from defects, and in the appearance of the finishei 
sheet, over that secured by the old-fashioned method 


Pear teR VIII 


ANNEALING 


still at a high temperature and must be 


| WE ) \s) d) J 


NX slowly cooled to permit its being placed 


Hay) \ 

(og 5 in the annealing oven. This cooling ef- 
ject is accomplished by the subsequent passing of 
he glass, while still on theflattening stone, through 
‘ooler sections of the oven, remote from the fire, 
until it comes into the section known as the “‘piling 
yven.’’ It is now sufficiently cooled to permit the 
workman to insert a large thin-pronged fork of 
\teel underneath the flattened sheet and to place it 
bn the rods that carry it through the annealing 
»ven, or lehr. 

The annealing of the glass consists simply in re- 
lucing the temperature of the heated sheet of glass 
slowly and gradually between two certain temper- 
atures, which constitute the critical range of tem- 
peratures for annealing, and then continuing the 
‘eduction of the temperature until the glass is suf- 
ficiently cooled to permit it to be handled. If the 
iglass is passed too rapidly through this critical 
‘range of temperatures, it will not be properly an- 


47 


48 Window Glass in the Making 


nealed, and it will be hard, brittle, difficult to cu; 
and it will not withstand ordinary handling : 
shipping without excessive breakage. In the orc: 
nary oven, these gradations of temperature are s} 
cured by advancing the sheet slowly on the rods 
the lehr from the piling oven to the discharge et) 
of the oven. 

In order to secure the best possible results in tl 
flattening and annealing, the American Windo 
Glass Company has recently made many changes i 
the old style flattening ovens and lehrs. The: 
changes make possible the production of windoy 
glass that is absolutely flat, so far as its use for con 
mercial purposes is concerned. It is as flat as gla: 
made by any of the flat sheet drawn processes. 

It is annealed so perfectly, as shown by Goverr 
ment tests, that it equals the annealing necessary i 
glass made for optical use, which requires the bes 
possible annealing. This results from the double ar 
nealing which the glass receives in this process. ] 
is annealed first during the drawing of the cylindet 
and again, in its passage through the annealing ove: 
or lehr. 


DIPPING AND WASHING 


When the sheets of glass are removed from th 
discharge end of the annealing oven, or lehr, the 
ate dipped and washed in a bath of muriatic aci 


a ee a 


Window Glass in the Making 49 


diluted with hot water. This is a very important 
step in the process. The glass, as it emerges from the 
lehr, has a considerable amount of free alkalies, or 


other foreign particles on the surfaces, occasioned 


by the process of manufacture. These foreign par- 


ticles must be removed; or otherwise, if the glass 


becomes wet, or sweats, they set up the chemical 
action that attacks the surface of the glass and 
causes it to discolor, z.e., fade, stain, or rust. The 
acid bath thoroughly cleans the surface of the glass 
of all these foreign particles. 


TYPICAL CUT 


¢ CExg D ert workmen here 


Truck ks are used to 
despatch shipment 


tatar LER IX 


CUTTING AND SORTING 


with a diamond ome in a cutting tool, but it 
can be cut just as well with a steel wheel. 

When the large sheets of glass are placed on the 
cutting table, the defects that have been made in 
all the different steps of the process become appar- 
‘ent. The skilled cutter sees these at a glance and 


'quickly cuts the sheet into the sizes and qualities 
desired, so far as the quality of the glass will per- 
‘mit. The cutter then “‘sorts’’ or ‘‘grades”’ the glass 
into the different qualities, according to the stand- 
ards of the company. 

The skill and judgment of the cutter in know- 
ing what defects are properly permissible, in any 
certain quality, are the most important factors in 
establishing a reputation for high quality glass. 
All the different processes of manufacturing window 
glass produce some poor glass, and the reputation 
of a firm for high quality glass is affected by the 


ve 


52 Window Glass in the Making 


amount of poor quality that is sent back to be re} 
melted, instead of being packed and sent out to the 
trade. 


SORTERS 


The various sizes, qualities, and thicknesses of the , 
cut glass are kept separate. All these are carefully 
examined again by skilled sorters, or inspectors 
who rectify any mistakes in grading by the cutters, 
and who are finally responsible for the finished 
product conforming to the Company’s standard of 
quality and thickness. 

In the grading of the glass, the quality is deter- 
mined by the defects—the glass of better quality 
naturally contains fewer and smaller defects than 
the glass of poorer quality. The rules for grading 
the glass will be found in the Appendix under the 
proper heading. 

After the glass has passed this inspection it is) 
sent to be packed. 


eee ER xX 


BOXES AND PACKING 


eS a tule, in this country, all window glass 
is packed in boxes containing the near- 

x 

) est number of lights or panes that will 


iacked in boxes containing as nearly as possible 100 
quate feet. Some of our specialties are packed in 
voxes containing 300 square feet. 

All our boxes have reinforcing cleats at the tops 
nd bottoms of the heads. They are made according 
0 a definite, uniform rule for the various sizes and 
hicknesses. The Company’s name, the number of 
he factory, and the size of the glass to be packed 
n the box are all neatly branded by a branding ma- 
hine on one of the heads of the box. 

For packing the glass in the boxes, we use long, 
pecially threshed, rye straw, which must be kept 
ibsolutely free from all moisture, or else the damp- 
1ess in it will attack the surface of the glass and 
sause the glass to fade or discolor. 

The glass, when finally packed, is thoroughly 
cushioned by the straw from contact with any part 
of the box. 


All glass is packed in long rye straws to 
insure safe transportation. 


CHAPTER XI 


LABELS, QUALITY SLIPS, 
AND BRANDING 


«(fy RANY dealers furnish a large amount < 


single thick glass toconsumers as doub. 
AX ) thick; and a great deal of glass of a lov 
h Kes grade of quality as being of a high¢ 
grade, because of the increased profit that can 
made by these substitutions. This would not kt 
possible if buyers had more knowledge of windoy 
glass and its process of manufacture. When deale1 
resort to that practice, they must change according 
ly the branding placed on the boxes by the man 


) 
ay ew WAS NS 


ufacturers. 

On each light of ““A” and “AA” quality gin pre 
duced by the American Window Glass Company 
is placed a label bearing a copy of the Company’ 
registered trade mark and certifying the qualit 
and strength of the glass. If the glass is not s 
labeled, it is of a lower grade than “‘A”’ quality. 

In each box of glass of a grade inferior to ““A’ 
quality, there is placed a slip of paper, known as : 
“Quality Slip,’’ on which is printed the Company’: 


Windows on a . 
Florentine Bridge — 


Gi fat I ite yi if (i WA te F 


Window Glass in the Making = 55 


ume and a certificate of the quality and thickness 
‘ the glass contained in the box. 

‘These labels and quality slips are a protection 
zainst the substitution of a lower quality for a 
igher quality of glass or of single strength for 
ouble strength. They are an insurance or guarantee 
) the buyer of the thickness and quality of the 
lass as packed by us. When a quality slip is not 
yund in a box of glass of the American Window 
lass Company’s manufacture, an explanation 
10uld be obtained to account for its absence. 

On the printed head of each box of glass of reg- 
lar quality, the packer stamps with a steel die, the 
tters designating the different grades of quality. 
AA” indicates the best quality; ‘‘A’’ the next best; 
id “B” the next lower grade. 

On boxes of ‘‘off-quality’’ glass, is stamped the 
ord “Fourth,” or the letter “‘C.”’ The latter indi- 
ites the poorest grade of glass packed. The Com- 
any s name never appears on boxes containing ‘“C” 
uality. 

If the glass is double thick, the word ‘“‘Double’”’ is 
amped across the printed head. Boxes not so 
latked contain single thick, unless otherwise 
iarked. 

The names of the cutter, packer, as well as a num- 
*r are stenciled on the printed head of each box. 
rom these it is possible to learn the exact date the 


Venetian 
Palace 


56 Window Glass in the Making 


glass was packed, and to trace it back through 
the different departments that handled it, to t 
machine on which it was made. In case of any co 
plaint or question regarding the glass, it is essent 
that the Company be informed of the marks 
the box. 


| Payee RX TI 


WAREHOUSING AND SHIPPING 


WBEYTER the glass is packed, it is taken to the 
ij Eo! Ns S) " 
¥Y warehouse to be stored or is sent out 


t badly ventilated warehouses are certain to have 
uch trouble with the glass fading, even though 
1e composition be of the very best. Everyone who 
as occasion to store glass for any length of time 
10uld inquire carefully into its analysis and ascer- 
in whether it has been dipped in the muriatic 
ath, so as to make sure that it can be stored safe- 
r. In case it is not of the proper composition or has 
ot been properly treated, it is certain to discolor or 
ide in a very short time when exposed to moisture. 

When shipping the glass, the greatest care is 
xken in loading the cars. The boxes must be se- 
ately wedged and braced to avoid shifting in trans- 
ort. Much unnecessary breakage is caused through 
morance or carelessness of shippers in the proper 
yading of glass. When a car is properly loaded, the 
lass will carry with practically no breakage in 
‘ansit, and is almost invariably received by the 
astomer in perfect condition. 


1¥ 5 


CHAPTER XIII 
DEFECTS IN GLASS 


MELTING DEFECTS 


=F the materials used in making the gla 
PR have not been of sufficient purity ar 
Vile 6 fineness, or are not well mixed in co 
MES E59 rect proportions, or if the furnace hz 
not been operated in a proper manner, the glass wi 
contain many defects that could have been avoidec 
Of the defects that may be found in any kind of glas: 
the following are the most important ones, occurrin 
in the melting and refining stages of the process: 
1. STONES—These may be of silica or clay 
resulting either from particles in the compositio 
too large to be melted, or coming from the furnac 
structure itself. They may also be caused by wron 
proportions of the ingredients, by devitrification, c 
by the improper operation of the furnace. No mai 
ter what the cause or the nature of them, the 
never should be permitted in the finished product 
They not only disfigure the glass but cause grea 
breakage. , 
2. SEEDS AND BLISTERS—Frequently, afte 


Windows in a 
Bavarian Town Hy 


Window Glass in the Making 59 


1e glass has reached the working zone, we find bub- 
les of various sizes, formed by the gases given off 
y the chemical action that takes place in melting, 
r by atmospheric air enclosed in the composition, 
thich, from various causes, have not been able to 
scape. Similar bubbles are also formed in working 
wrough the carelessness or incompetence of the 
rotkmen in permitting small portions of air to be 
aveloped in the glass. In the subsequent stage of 
1e process these bubbles are elongated to a greater 
r lesser extent, taking on an elliptical shape ac- 
ording to their size and the process of manufacture. 
he very small ones are called ‘‘seeds,’’ while the 
irger ones are called ‘‘blisters.’’ 

3. WAVES OR REAM—These are wave-like 
steaks or bands visible in the finished glass when 
iewed at a sufficiently sharp angle or in a reflected 
ght. They appear to be of a slightly darker green- 
h tint, and are slightly thicker than the other por- 
‘ons of the glass. They indicate a lack of homo- 
eneity in the glass, caused either by irregularity in 
ne heat of the furnace or by a change in the kind 
t proportions of the materials filled in the furnace. 
carcely any glass is entirely free from them. Some- 
mes they are heavier and more numerous than at 
ther times. When they are quite light they are very 
ifficult to detect and cause very slight distortion; 


Windows in 
a French Chateau 


= 


60 Window Glass in the Making 


but when they are heavy, the distortion is consid) 
able. This defect is properly called, ‘“‘ream.”’ 
4. CORDS AND LINES—“‘Cords”’ is the nay 


given to threadlike streaks often found in glaj, 
that appear to be of a different nature from the mip 
portion of it. They hinder the vision through ti 
glass. Sometimes they cover the entire piece, a} 
at other times only a portion of it. | 
They are caused either by a too sudden lowerip 
of the heat of the furnace or by the chilling of tk 
glass that is being ‘‘worked up’’ into the finishi 
product. ) 
In the hand-blowing process of manufacture thj 
usually extend around the cylinder in more or lis 
irregular fashion. In the mechanical process, thi 
extend in parallel lines in the direction in which t) 
glass is drawn and are sometimes known as “‘lines) 
5. STRINGS—These are fine transparent threals 
of glass that are not made in the ordinary meltii 
but which come from the vitrifying of some porti| 
of the furnace structure. They are of an entirely d/ 
ferent nature from the body of the glass and a 
readily noticeable when they have been incorp 
rated into the finished product. | 
6. KNOTS—Knots are small particles of gla 
that have not been as thoroughly melted as the re| 
of the glass. They are of the same color as the gla 
Windows— 
Mt. Athos, Greece 


Window Glass inthe Making 61 


put noticeably of a different nature. Sometimes they 
are entirely clear, like very small glass beads; at 
other times they may have a grain of sand imbedded 
n them. It is a defect quite similar in character to 
stones, except that the stones are not vitrified like 
‘he knots. They should never be allowed in the 
inished product because they disfigure the appear- 
ance of the glass and cause excessive breakage. 


FLATTENING DEFECTS 


Formerly many defects were introduced into the 
zlass in this step of the process, though our recent 
nventions demonstrate that none of them are in- 
1erent or necessary; all result from either careless- 
1ess or lack of skill by the workmen, or failure to 
ontrol the process scientifically. 

The following are the principal defects found in 
ome of the flattened glass: 

1. BURN—This results from running the oven 
it too high a temperature or permitting the glass 
© remain too long on the flattening stone. This 
auses the glass to have a faintly pimpled or slightly 


is glass that has been marred by the rolls in some 
f the sheet drawn processes. 
2. WRINKLES—These resemble corrugations 


anded appearance. \ 
When glass is burnt it has the same appearance \ 
\ 
ed 


Caneo—an old harbor is 
of Crete 


Or 2 ee ae 


we at wd ‘i y 
4 aly alamo 


62 Window Glass in the Making 


in the glass caused by the sheet not having been « 
tirely ‘‘ironed out’’ on the flattening stone. 

Glass containing wrinkles never should be pack« 
because they always cause breakage. 

3. COCKLES—These are slightly raised plac 
on the surface of a sheet of glass, caused by the fa 
ure of the flattener to “‘rub out”’ properly the fl: 
tened sheet. 

When these are found in cylinder made glass, tl 
defect is identical in appearance with the humps a 
depressions found in glass made by some of the she 
drawn processes. 


OTHER DEFECTS 


SCRATCHES—The most common defect in : 
glass is scratches. They are found in every kind 
glass that is made, regardless of the process of ma 
ufacture. From the time the glass passes from t. 
plastic state to the solid, it is liable to be scratch 
at every stage of the process and with every ha 
dling. They are usually caused by the lack of care 
skill on the part of the workmen, but sometimes | 
the process of manufacture. 

They are on the surface of the glass. Some are ve 
large and heavy, while others are very fine, ligt 
and almost imperceptible except to the train 
eye. Few realize how easily glass can be scratch 


tia ie itil 


Window Glass in the Making 63 


by drawing a hard, rough substance across its sur- 
face, or how the scratches disfigure it. More good 
glass is spoiled by scratches than by any other 
defect. 
_ FADED GLASS (Stain or Rust)—AIl window 
glass, regardless of its composition, is susceptible 
to attack by chemical action that begins with mois- 
ture, and will therefore discolor or fade, no matter 
‘whether or not it has been previously dipped or 
washed in the dilute muriatic acid bath, unless the 
acid bath is sufficiently strong to cause the surface 
of the glass, when dried, to show an acid reaction. 
Glass not so treated will discolor or fade very much 
more quickly than the glass that has been so treat- 
ed. If the acid bath is too strong, it produces a 
_“hum,”’ or cloudy appearance on the surface of the 
glass, which renders it very difficult to detect the 
defects. Sometimes manufacturers use an excessive 
amount of the acid to hide the poor quality of their 
glass. 

When moisture occurs on the surface of the glass, 
either from sweating or from any other cause, and 
it comes in contact with ordinary dirt or carbon, it 
sets up a chemical action that attacks the surface 
of the glass and causes the discoloration that we 
call “‘fade.’’ This is sometimes called “‘stain’’ and 
sometimes called ‘‘rust.’’ It manifests itself at first 


64 Window Glass in the Making 


by an iridescence on the surface of the glass, a 
though carbon oil had been placed on it, whic 
dulls its lustre. If the chemical action continue 
a sufficient time, the glass then takes on a froste: 
appearance, which will gradually increase,until th) 
glass finally becomes opaque. Glass containing toi 
much soda or too little lime will fade very quickly 

Careful housewives have spent many hours o 
wasted efforts trying to wash or rub off the oil-lik) 
stain, caused by ‘“‘fade,’’ on the glass in the win 
dows of their homes. In the early stages of fade, th! 
discoloration can be removed only by dipping thi 
glass in an acid bath; but if the glass has becom 
quite opaque, nothing can be done to restore it! 
former brilliant surface. | 


Sener 


' 


ie lek XIV 


WINDOW GLASS WAVE 


‘at a sharp “ae between the line of sight and the 
glass. It results from the fact that the outside surface 
of the cylinder is longer than the inside; and when 
flattened, it must be compressed, as it were, within 
the same space as the inside surface. It is not a defect. 

All window glass, no matter by what process it 
is made, presents an appearance practically identi- 
cal with that caused by the window glass wave, 
when it is viewed at the same angle. In some of the 
sheet drawn processes it is much more pronounced, 
and causes greater distortion. 

Prior to the invention of the sheet drawn proces- 
ses, it was believed that glass drawn in sheet form 
would have an entirely different appearance from 
cylinder made glass. Unfortunately, the expecta- 
tions of the inventors were never realized. All such 
glass still retains the characteristic appearance of 
cylinder made window glass. In the sheet drawn 
processes this results from slight temperature varia- 


65 


66 Window Glass in the Making 


tions in the bath of glass or lack of homogeneity 


F 
| 


When the plastic glass is subjected to the drawin| 
and stretching strains, these differences in the glas 
temperatures produce a more or less wavy appeat 
ance in the drawn sheet, similar to that of th 
window glass wave in cylinder made glass. 


CHAPTER XV 


OUR PRODUCTIONS 


RG 
Microscopic Slides 

Lantern Slide Glass 

Photo Dry Plate Glass 

Diagnostic X-Ray Glass 

16-0z. Picture Glass 

Single Strength Glass 

Double Strength Glass 

26-0z. Glass 

29-0z. Glass 

34-0z. (42 millimeter) Crystal Sheet 

39-0z. (%.6”, or 5 millimeter) Crystal Sheet 


We also produce the following ‘‘Processed Glass’’: 
Ground Glass 
Chipped Glass, 1 Process 
Chipped Glass, 2 Processes 
- When glass is described as of a certain weight, it 
means the weight per square foot of that thickness. 


67 


i, Fi e 
oy Ea 
a 
igi 


ne 


68 Window Glass in the Making | 


A square foot of window glass one inch thic 
weighs, on the average, thirteen pounds. 

All of the foregoing productions are of the sa 
composition and are made by the same process 
They differ from one another only in the thickness 
flatness, and selection of quality, according to th 
special purpose for which the glass is to be used. | 


MICROSCOPIC SLIDES, LANTERN SLIDE 
GLASS, PHOTO DRY PLATE GLASS, 
AND DIAGNOSTIC X-RAY GLASS 


The above named productions are all of the sam 
general class. They are much thinner than othe 
glass, and they require absolute flatness and thi 
very best quality. We are the only manufacture 
in this country who can produce such glass. Year: 
ago attempts were made to produce it here by thi 
hand blowing method, but without success. Ir 
1913, after some years of experimenting and ar 
enormous expenditure of money, we began its pro: 
duction on a commercial scale, and succeeded in pro- 
ducing a quality superior to that of imported glass. 

Shortly after the close of the war, the Europear 
manufacturers resumed the production of this glass 
and sold it in this country at prices with which we 
could not compete, notwithstanding our superior 
quality. As a result, we were obliged to curtail very 
greatly our production of this kind of glass. 


Windows on a by-street 
of Constantinople 


Mf . 
ie 


a, 


Window Glass inthe Making 69 
When our country went into the war, we were the 
only manufacturer here that could make the kind of 
zlass required for eye pieces for gas masks. These 
were made of very thin glass, cut into circles about 
2% inches in diameter. They were subsequently 
slaced together in pairs with a thin coating of 
iquid celluloid between them and were then sub- 
ected to very great pressure. If the glass was not 
serfectly flat, or was not cut with a perfectly smooth 
sdge, the celluloid would not bind the two circles 
jogether sufficiently to permit them to be used. 

This process had the effect of rendering the glass 
“non-scatterable’’; that is, pieces would not break 
off and fly, when it was struck a very heavy blow. 
Jnder the concussion the glass would crack, but 
ull the particles would remain firmly held together 
oy the celluloid binder. 

Through the patriotic assistance of men, women, 
ind children of a Red Cross Unit during the war, in 
olunteering to learn to cut this glass when other 
abor was not to be had, we were able to furnish 
17,000,000 of these circles for the use of our army 
und the armies of our Allies. 


16-OZ. PICTURE GLASS 


We are the only manufacturer making 16-oz. 
Picture Glass in this country. Prior to our making 


2 gms - 
Ae f EZ 

“ ; 
en jngam ea saat i 
eh am a0 koro \ty 0 
Jl ganna amo 


Windows at Bastia, 
@ port of Corsica 


Wake 


5 —_ 
——— a 
Taare 

“at San : 
re 54 


70 Window Glass in the Making 


it, all such glass was imported from Europe, b 
our glass proved to be of such superior quality thi 
very little is now imported. It is thinner than sing 
strength window glass, ranging in thickness fre 
1214 to 14 lights to the inch, but is graded to 
much higher standard of quality. It is sold in th 
grades, under the trade designations of ‘‘Superfine 
which is the best quality; ‘‘Selected,” which is 
very fine quality but not quite equal to the be 
and “‘Commercial,” which is a somewhat poor 
grade but superior to ““B” quality window glass. 

In producing it great care must be taken at eve: 
stage of the process, and only the most skilled m¢ 
handle it. As a result, it has the even thicknes 
flatness, smoothness of surface, lustre, and freedo 
from defects so necessary in glass used in framir 
high grade pictures. 

It is purposely made thinner than ordinary wit 
dow glass in order to transmit more light than tk 
thicker glass. Its exceptional quality makes it als 
especially adaptable for usein mirrors, French door 
and for any other purposes that require glass of vet 
attractive appearance rather than of great strengtl 

In order to protect the buyer of this glass again: 
substitutions, a special label is placed either on eac 
light or on the paper that is placed between tk 
lights in all boxes of ‘‘Superfine”’ and “Selected 
quality. 


Pagoda of the - 
Sung Dynasty 


Window Glass in the Making 71 


SINGLE AND DOUBLE STRENGTH 
WINDOW GLASS 


More than 90% of all the window glass used an- 
ually in this country is in these two thicknesses. 
he single strength, as its name would imply, is 
yuch thinner and consequently lighter in weight 
aan the double. That is really the only difference 
dfar as the glass itself is concerned. Greater care 
s always taken with the double strength glass and 
he most skilled men are used in making it, on ac- 
ount of the increased difficulty in handling it. 
Vhile the rules for grading are the same for both 
hicknesses, yet the double strength is apt to appear 
lightly better than single strength. The greatest 
ossible care is used with both of these thicknesses, 
nd there should be no material difference in the 
tading. The thinner glass should be used in places 
vhere the strength or thickness is not an important 
actor; but where the windows are exposed to very 
avy winds, it is safer to use the double strength 
lass. 

There is considerable difference in the prices of 
he two thicknesses—the single strength naturally 
osting less. The buyers should be able to distin- 
ish between the thicknesses. After the glass has 
een glazed in the sash, it is very difficult to detect 
he difference. By tapping the glass with some hard 


A Government Building 
in Rio de Janeiro 


72 Window Glass in the Making 


substance the thinner glass resounds more faintly 
than the double thick. 

Complete details as to the thickness, flatness, and 
the rules for grading the above named production: 
will be found in the Appendix under the prope 
headings. F 

Those who use our glass for whatever purposes 
window glass is required, can be assured of having 
“The Best Glass’’ made. In the evenness of its 
thickness, in the flatness of its surface, in the bril: 
liance of its polish, in its durability and physica 
strength—it is not equalled by window glass mad¢ 
by any other process. 


26-OZ. AND 29-OZ. GLASS 


These two kinds of glass differ from the regular} 
double thick glass in their thickness, special flat- 
ness, and higher standard of quality. Those tre- 
quiring glass slightly heavier than double thick 
and of a specially fine quality, will find that this 
glass will meet their every requirement. ~ 


CRYSTAL SHEET 
2k 34-OZ. AND 39-OZ. OR 346” GLASS 


We introduced our 34-0z. and 39-oz. or %e 
glass to the trade as ‘‘Crystal Sheet,” a really beau- 
tiful glass. Its quality is so exceptional, its flatness 
so wonderful, and its uniformity of thickness so 


uy 


£3 “iff 4 ) 
a ia as (Sas 
SNS ac 
Tee are en ae ey re RA, 
ALL ry ( . 


" 
oo a 
x finn 2 if 3 


a \ ) ay 


NS 
Ne 

7  India—the 
Balconies of Lahore 


aa 
ford 


se 


Window Glass inthe Making 73 


wfect that it is adaptable for many purposes for 
hich plate glass has ordinarily been used. In the 
aaller sizes 1t presents such a fine appearance that 
ly an expert can distinguish it from plate glass. 

It is suitable for glazing office buildings, hotels, 
spitals, public buildings of all kinds, and dwell- 
gs, in which not only the appearance of the glass 
very important, but the thickness and strength as 
ell. Large quantities of it are used in automobiles, 
1 windshields, bodies, and accessories. It is also 
sed for typewriter keys, clock faces, showcases, 
yunters, shelving, car windows, small mirrors, 
* and table tops, and other furniture. 

All this glass is handled with special care. It is 
acked with paper between the lights, and every 
ght is labeled to identify the quality and thick- 
ess for which it is sold. 

Being thinner and consequently lighter in weight 
ian plate glass it does not require window sash of 
yecial construction, nor the use of extra heavy 
ish weights, which are necessary when using plate 
lass. It is also much cheaper than plate glass which 
sts about one-third more than our Crystal Sheet. 
Recently, large amounts of thick window glass 


ave been imported from Europe, in competition Syn 

ith our Crystal Sheet glass. Some of it is sold as emul | a= 
meu ; WN eeaat 

44 millimeter glass, corresponding to 34-oz. glass; é WEE ; 
ad some is sold as 5 millimeter glass, which corre- Miesisae\" 

f= Ln a | 

Windows in ; Wen 

Guanajuato, Mexico Wi aw 

B eee, 

— 


ae 


74 Window Glass in the Making 


sponds to 39-oz. or %6” glass. This foreign glass i 
made by a sheet drawn process that requires a dif 
of good window glass. Analyses show it to be high 
in soda, low in lime, and low in silica, and it there 
fore lacks the strength, density, and resistance t 
fade or stain of our glass, and it will not warehous 


as well. 


PROCESSED GLASS 


This is either in the form of ground glass o 
chipped glass. Ground glass is made by sandblast 
ing one surface of clear window glass, which give 
it a slightly frosted appearance that renders it sui 
able for obscuring purposes. 

This glass is often subsequently coated on thé 
ground side with glue, and placed in heated drying 
kilns. In drying, the glue “‘cracks off,”’ taking wit 
it thin particles of the surface of the glass, produc 
ing a chipped effect. When the glass has been suk 
jected to this process only once, it is known a 
‘‘chipped one process,’’ but when the process is re 
peated, it is known as “‘chipped two processes.”’ | 

The chipping gives the glass a very attractive an 
unique appearance. The surface appears to hay 
leaves of all sizes, kinds and shapes, cut into th 
glass with all the beautiful veinings seen in fores 
leaves. The chipping, of course, hinders the trans 


Window Glass in the Making =_75 


nission of light. Very beautiful effects can be pro- 
luced with this glass, either by itself or in com- 
ination with ground glass. It is very suitable and 
\ost attractive when used in door lights, transoms, 
abinets, screens, partitions, and windows. 


CHAP TERA ve 


COMPARISON OF GLASS 


\ BY glass is subject, we wish to call thé 
¥4/@.4 reader’s attention to the fact that all} 


Those described under the heading, “‘Melting De 
fects,’’ are common to all kinds of glass, without 
any exception. In addition, each kind is subject top 
certain other defects that are incidental or character- 
istic of the process of manufacture. | 


OTHER WINDOW GLASS 


Comparing window glass made by different proc- 
esses, one will find the same kind of defects in 
each, though they may result from different causes. 
One process will accentuate certain kinds of de- 
fects, while other processes accentuate others. The 
process is never an argument as to the quality of 
the product. That, as we have seen, depends largely 
upon the methods of manufacturing. | 


Some processes of manufacturing window glass 


76 


Window Glass inthe Making 77 


ave certain advantages over others. For the most 
art these are confined to an economy of labor, fuel, 
r both. Our process not only effects these econo- 
lies, but with our manufacturing methods it en- 
bles us to produce a larger percentage of glass of 
ae higher grades of quality than any other process 
1 use throughout the world today. 

On account of the composition we use, our 
ethods of drawing and blowing, and the double 
nealing which the glass receives, our glass is less 
tittle and has a better nature than any other win- 
ow glass. 

In the Appendix we have inserted tables showing 
e tensile strength and modulus of rupture of our 
lass. A comparison of these tests with similar 
sts of any other window glass, plate glass, or 
olled glass, proves that our glass is stronger per 
nit of thickness than any other glass. 

In conclusion, the superiority of the American 
Vindow Glass Company’s glass over any other 
vindow glass may be summed up in the following 
losing sentences: 

It is the most durable glass. 

It is the strongest glass. 

It is “The Best Glass.” 


APPENDIX 


U.S. Government Master Specifications 


with our comment 


(U.S. Government Specifications are printed 
in Italics) 


APPENDIX 


Cj WING TO THE FACT that single strength 
® window glass costs much less than the 
> double strength glass, and glass of a 
Zy lower grade of quality costs much less 
han glass of a higher grade, some dealers taking 
dvantage of the fact that few buyers of window 
lass are familiar with the rules for grading glass, 
esort to the practice of substituting the thinner 
lass for the thicker glass, and the lower grades of 
uality for the higher grades. This practice has 
teatly increased during the past few years on ac- 
ount of the severe competition in the business, 
nd innocent purchasers suffer as a result of it. 

Buyers heretofore have been unable to protect 
hemselves against these substitutions, by reason of 
ot having any positive and authoritative infor- 
ration regarding the thicknesses of window glass 
nd the rules for grading it. This information is now 
urnished by the United States Master Specifica- 
ion, prepared by the Bureau of Standards, after 
ery exhaustive study and research. It is known as 


orth ; in this eee 


81 


82 Window Glass in the Making 


This Specification was officially adopted by t 
Federal Specifications Board on April 1, 1924, f 
the use of the Departments and Independent Esta 
lishments of the Government in the purchase 
flat glass for glazing purposes. It is a valuable gui 
for manufacturers, architects, jobbers, dealers, g] 
ziers, users, and buyers generally, regarding the siz 
thicknesses, qualities, and rules for grading winde 
glass. A careful study of it will qualify one to jud 
window glass, and to know whether the glass ft 
nished is of the thickness and quality for which 
was bought. 

Since this ‘‘Master Specification’’ was publishe 
number of changes have taken place in the charact 
of the window glass produced in this country, ai 
in the designation of some of the qualities. Atte 
tion is called to these changes under the appropria 
headings. We have also added such explanato 
notes and comments on the ‘‘Master Specification 
as will give the reader a clearer understanding 
the subject. 

Those who wish to buy window glass of t 
highest quality, that conforms in every way tot 
“Government Specification,’’ should specify t 
American Window Glass Company’s brand—‘‘T. 
Best Glass.’’ It is the best glass for the for 
teen reasons we have outlined at the end of tl 
pamphlet. . ‘ 


* 


Window Glass in the Making 83 


Architects who desire ‘The Best Glass’’ for the 
uildings they design should specify it as follows: 
“All window glass to be used in this building 
shall be the American Window Glass Com- 
_pany’s make or equal thereto, and shall be 
(here specify the thickness and quality of glass 
desired), All “A” quality glass furnished must 
have the manufacturer’s label on each light.” 


‘the American Window Glass Company’s glass is 
pecified, the company will follow up the job when- 
ver requested, without any expense to the party 
equesting it, and report whether the glass furnished 
xc kind, quality, and thickness specified. 


Definition of Clear Window Glass” 

“Crear Winpow Guass’’—Transparent, relatively 
bin flat glass having glossy, fire finished, apparently plane 
nd smooth surfaces, but having a characteristic waviness 
f surface which is visible when viewed at an acute angle 
r in reflected light. 

“Crear Winpow Guass’’ és made at present by hand 
lowing, or by machine blowing and drawing into cylinders 
nd flattening, or by drawing directly into a sheet, the sur- 
ace finish being that obtained during the drawing process.”’ 
The ‘‘characteristic waviness” referred to in the 
oregoing definition should be distinguished from 
he heavy waves frequently noticed in glass of poor 
uality. These have the appearance of wide bands 


® 


rc 


84 Window Glass in the Making 


or streaks extending across the sheet, of a slight! 
darker tint than the main body of the glass. It is 
defect called “ream” and causes considerable di 
tortion. 


“General Principles Involved in 
Grading Glass” 


“All flat glass contains some imperfections and t, 
principle employed in grading is to exclude all defects th, 
would be objectionable in a given grade. This is difficu 
to do since there are no sharp lines of demarcation betwe 
grades, and experienced inspectors will differ in judgme 
as the quality of the glass approaches the limits of t 
grades. Small lights must be quite free from imperfectios 
as compared with larger ones, and the center of any she 
should be clear whereas the edges may contain more pt 
nounced defects.”’ 


“Central Area of the Sheet” 


“In window glass the central area of the sheet is co 
sidered as being a circle having a diameter equal to ha 
the width of the sheet or an ellipse having one diamei 
equal to half the length of the sheet and the other diamei 
equal to half the width of the sheet.”’ ; 


Terms 


“The following terms shall be used in specifications. 


applying to clear window glass: seeds, blisters, ‘? 
burns, scratches, strings, cords, stones.’ | 


To these should be added ‘‘ream’’ and “cockles 


pa 
be 
3 


Window Glass inthe Making 8; 


Fr: Ja ap 
Definitions, causes, and brief descriptions of these 
arious imperfections are all set forth in the chap- 
of ‘Defects in Glass.”’ 


Yefects Prohibited in All Grades 


Stones, knots, very heavy lines or cords, long or 
uised blisters, wrinkles, heavy burn, foreign par- 
icles adhering to the surface of the glass, deep 
sratches, fade or stain, and in general every defect 
dat might cause excessive breakage is prohibited 
1 all grades of window glass. 


Method of Examination” 


“The method of examination is described in these speci- 

cations im order to make the results more uniform and 
efines the condition under which glass should be exam- 
ued because the distance from the glass, the angle between 
0¢ glass and the line of sight, and the intensity of light 
I) affect the visibility of imperfections. 
“These specifications should be interpreted by examining 
be glass in the following manner, with reference to the 
efinitions of defects listed in the glossary (U. S. Speci- 
cations): 

“The glass should be examined when placed in a position 
imilar to that of a glazed light with the observer's eye on 
Tevel with the center of the sheet, and looking through the 
lass from a distance of about 36 inches into the light from 
clear sky without any sun or any close background. 

“The visibility of waves, lines or cords depends chiefly 
pon the angle of observation, and the intensity of these 


86 Window Glass in the Making 


3 
defects can be classified on this basis. The values given fi 
angles are the angles the line of sight makes with the she 
of glass when in a vertical position. Slight tovernem 
the head horizontally through an angle of two or thr 
degrees will make waves or lines more perceptible.” i 
“Acceptance or Rejection” j 

“Acceptance or rejection of a shipment or delivery sha 
be based on an examination of the following quantities: 

‘* For orders of 100 lights or less, all shall be examine 
for orders of 101 to 500 Lights at least 50% shall be 
amined; fororders of 501 or more lights at least 25% sha 
be examined. Boxes shall be selected from the shipme 
at random. q 

“Tf not more than 10 per cent of the lights examined a 4 
below quality, the shipment shall be accepted provided ti 
lights below the specified grade are not distinctly below ti 
none, limit of the next lower grade. 

“Tf, however, an entire shipment of 500 lights or ma 
examined, not more than 5% may be below quality.” 


The foregoing specification was drawn to cov 
the delivery of glass ‘‘to the job” in small lots. } 
carload shipments it is customary to judge the gla: 
by the quality found in 25 or 50 boxes of the s i 
ment, selected at random. 


| “Specifications for Clear Window Glass 
for Glazing” 


“Clear window glass for glazing is made in several ¢ 


es Rong a 4 


Window Glass in the Making 87 


ferent qualities and in the varying thicknesses shown in 
Table 1, page 95. 

“Single strength and double strength window glass is 
regularly supplied in two standard qualities, known as A 
quality and B quality. A limited amount of this glass, 
known as AA quality, which is especzally free from defects, 
is sometimes selected for special purposes and may be spec- 
ified if desired. It must be borne in mind, however, that the 
total amount of AA glass produced by the manufacturers 
does not exceed 3% of the total amount of window glass 
produced. 

“There is also a limited amount of single strength and 
double strength glass produced in a quality inferior to B 
quality, and is known as Fourth quality. The amount of 
glass produced in this quality also represents a very small 
percentage of the total window glass produced. 

“A quality of single strength glass inferior to Fourth 
Quality is also produced in very limited quantities, and is 
known as C quality. This is the lowest grade of glass that 
15 packed and marketed in this country. 

“Window glass is also produced in thicknesses heavier 
than double strength, and according to its thickness it is 
classified as (1) 26-02. glass; (2) 29-02. glass; (3) 34- 
0x. glass; (A) 39-0z. or 3A” glass. 

_'26-0z. and 29-02. glass are produced only in A and B 
Be slisies. 

_ "34-02. and 39-0z. or 346" glass are produced in glazing 
and factory run quality.” 


88 Window Glass in the Making 


RULES FOR GRADING 

“AA” Quality : 
This quality requires the best grade of glass ob 
tainable, but it does not require perfect glass or sub- 
stantially perfect glass. As a matter of fact, it is | 
impossible to produce flawless glass of any kind, in| 
large sizes or quantities. The finest glass made only) 
approximates flawless glass; and the larger the di-| 
mensions, the more flaws it will contain. | 
Defects of various kinds are permissible in this) 
quality, but they should be very slight or not dis- 
coverable except on close inspection. 
In general, the center of each light must be prac-| 

_ tically free from defects. Each light must be viewed) 
as a whole, and not judged by single defects in ‘7 
ferent parts of the light. | 
On account of our very high standard of grading, | 
it is impossible for us to produce this quality in| 
sufficient quantities to enable us to fill orders for it| 
quickly. Buyers who insist upon having it must ex- 
pect greater delay in the shipment of their orders 
than when ordering the other qualities. | 
The price of this quality is considerably hight 
than that of ‘‘A” quality. This is made necessary by 
the large amount of waste occasioned in manufac- 
turing this quality and by the additional lab 
cost involved in producing it. 


Window Glass in the Making 89 


“A” Quality 

“The defects permitted in this quality are faint strings 
or lines, slight burn, small seeds, small blisters, and 
light scratches. 

“No light shall contain all of these defects, and those 
present may not be grouped when in the central area of the 
sheet. 

“Strings, lines, or burn specks shall not be of such inten- 
sity that they are visible when observing the sheet at an 
angle greater than 30 degrees between the line of sight and 
the glass. 

“Waves shall not be visible at an angle greater than 20 
degrees with the glass. 

“Blisters shall not exceed 14 inch in length unless they 
occur near the edge of the sheet. 

“In general, the central area of the light shall be practt- 
cally free from defects, and the appearance of the light as a 
whole shall be such that there is no perceptible interference 
with the vision as long as one 15 not looking through the 
glass at an acute angle.’’ 

It is exceedingly difficult to judge defects by view- 
ing the glass at a specified angie, for the reason that 
the slightest motion of the head or the eye will 
change that angle. Moreover, the eye takes in such 
a large portion of the surface, that one part of the 
sheet will be viewed at one angle and another part 
will be seen at a very different angle. 


rl 


90 ~=©6- Window Glass in the Making 


The limit of the angle at which waves are visible 
is too low. There is no good reason why waves or 
ream may not be visible at as large an angle as 
strings and lines without unduly affecting the 
quality. _ 

“A” quality should be used in windows of all 
buildings the appearance of which is an important 


used even in the finest buildings is either “’B” quality 
oreven a lower grade, becauseit is cheaper, although 
doubtless a very large percentage of it is specified 
in ‘A’ quality. A building glazed with the poorer | 
grades of glass does not present the appearance of 
one glazed with “A” quality. : 

No specific rule can be laid down as to the size of 
any defect permitted. A defect too large for a small 
light might be permitted in a much larger light. 
The location of the defects also determines the nu m- 
ber and size permitted. Seeds and small blisters that 
would not be permissible in the center of the light 
would be allowable if remote from the center. 

To protect the architects and buyers who desire 
to use the best quality of window glass, we 
adopted the practice of putting a label on each 
light of “A” and “AA” quality. For their further 
protection the architects and buyers should be able 
to distinguish the inferior see of glass when 
they see them. 


Window Glass in the Making gt 
RB” Quality 


“This quality admits of the same kind of defects as A 
quality, but they may be larger, heavier and more nu- 
merous. 


“Occasional scattered blisters not more than V4 inchlong 
may occur over the central area of the sheet. Larger blisters 
up to 1 inch in length may occur about the bordering 
areas. 


“Waves should not be of such intensity that they are vis- 
ible when observing the sheet at an angle greater than 45 
degrees with the glass, unless on the border. 


“Burn spots may be visible when looking directly through 
the glass, but they must not cause any appreciable de- 
pression and the speckled appearance must not be so great 
as to interfere with vision when examining the glass in the 


Specified position.’ 


In general, the defects permitted in this glass are 
SO prominent as to attract the attention of the casual 
inspector at once; but they should not be so nu- 
merous as to prevent a considerable portion of each 
. from being reasonably free from them. 


In buildings where the cost of construction is the 
most important factor, ‘“B’’ quality glass should be 
used. However, great care should be taken to obtain 
the highest standard of ‘‘B’’ quality. There are many 
factories turning out glass branded ‘‘B’”’ quality 


92 Window Glass in the Making 


which is really only “Fourth,” and even “‘C”’ qual- 
ity. Such brands are always sold at lower prices than 
our “‘B” quality, but the difference in prices does not 
compensate for the great deficiency in quality of the 
cheaper glass. Buyers should insist upon having the q 
American Window Glass Company's quality slip 
in each box of “‘B” quality. 


“Fourth” Quality 


Since the Master Specification was published, the 
amount of single strength and double strength glass 
produced in this quality has increased very greatly. 

Glass of this grade is known to the trade as ° off 
quality”’ glass, and is not subject to rejection on ac | 
count of defects. No very definite rules can be laid 
down for the grading of this quality. Glass that is 
too poor for ““B’’qualityis usually classed as “Fourth” | 
quality, unless the defects are so many and so glar- 
ing that they leave practically no portion of the’ 
light free from them, in which case it is classed as| 
“C” quality. It may contain many prominent defects 
that will hinder the view or distort the appearance | 
of objects viewed through it. These include blisters, 
heavy lines or cords, ream, cockles, and heavy burn. | 

On account of the disfiguring and distorting de- 
fects found in glass of this quality, it should never 
be permitted to be used in dwellings, schools, or 
other buildings where the appearance of the build- 


Window Glass in the Making 93 


ing or the vision of the occupants is a factor. It sells 
at very much lower prices than “‘B’”’ quality, and 
much of it is substituted for ‘‘B” quality in window 
sashes that are sold in markets where ‘‘price is the 
only consideration.’’ 
“C” Quality 

This is another type of ‘‘off-quality’’ glass, of a 
lower grade than “Fourth” quality. It is really rub- 
bish that should be remelted instead of being sent 
out to the trade. Such glass is usually not fit for 
use for any purpose except hotbed sash, and it is gen- 
stally produced only in single strength, in a limited 
aumber of small sizes, none of them larger than 
12x 18. 
It is sold at very much lower prices than‘‘Fourth” 
quality, and is frequently substituted for ‘“‘Fourth’’ 
quality, or even ‘‘B’” quality in markets where the 
buyers do not have sufficient knowledge of window 
glass grading to enable them to detect the differ- 
once. 
It may contain any and all the defects found in 
window glass, except such as will cause excessive 
breakage. 
— “C” glass is not subject to rejection or claims on 
account of defective quality. It always shows a 
much higher breakage in shipment than glass of 
the better qualities. 


94 Window Glass in the Making 


All 26-0z., 29-0Z.;3 4-0z., and 39-02. or 346” glass 
Pe by us : known to the trade and sold a 
“Crystal Sheet.’ ig 
The 26-oz. and 29-0z. glass is produced i in “A” ot 
**B”’ quality only. 
RULES FOR GRADING HEAVY SHEET 
WINDOW GLASS OR “CRYSTAL SHEET”: 
“Heavy Sheet Window Glass Glazing Quality’ ; 
“The same specifications for selecting provided for A 
quality single strength and double strength glass shall 
apply.” 7 
“Factory Run Quality” 7| 
“This quality is the run of glass as produced by the 
factory. It may contain glass of very good quality a 1d 
some glass of very ordinary quality. However, the glass 
that contains heavy cords, lines or strings over the entire 
surface, raised blisters, cap strings, stones or batch par- 
ticles causing a rough surface, or depression, or having its 
surface covered with heavy burns, wrinkles, deep scratches 
or stone, shall not be included in this quality.” | 
The terms used by us to designate the qualities of 


next best quality. The latter embraces glass of all 
qualities as produced, without selection, except that 
glass containing very large or very many disfiguring 


Window Glass in the Making 95 


if 
XG 
: 
= 


Bcts, such as those described under the heading, 
‘Factory Run Quality,’’ is culled out as ‘‘off- 
yuality”’ glass and sold as ‘‘OB” quality. 

Stock sheets are sold as ‘‘Selected Quality Stock 
Sheets.’ This includes the sheets of glass of all 
qualities just as produced, except those containing 
30 many or such large defects, as would render it im- 
possible to cut up the sheets to advantage. These 
poor quality sheets are set aside and sold as ‘“OB” 
quality stock sheets, at materially lower prices than 
= ‘Selected Quality Stock Sheets.” 


“Table 1—Tolerances in Thickness and Average 
Weight of Clear Window Glass.”’ 


be Thickness Number of Average 
es in lights per weight 
2 inches inch in a 
e Min. Max. Min. Max. eS. 
Single Strength ...... .080 .100 10.5 12.0 18.5 
Double Strength ..... 111 .125 8.0 9.0 24.5 
26-0z. Glass......... His 2135" 7.5 8.0-26.0 
29-0z. Glass......... 135 .148 6.5 7.0 29.0 


34-02. Heavy Glass... .150 .175 6.0 6.5 34.0 
39-0z. Heavy Glass.. .176 .205 5.0 5.5 39.0 
Microscopic Slides... 038 .045 22 to26 9 


Lantern Slides ea .050 .055 18 #020 11 
Photo Dry Plates.... .062 .071 14 #016 14 
X-Ray Plates ees .071 .080 12% to 14 16 


16-0z. Picture ....... .071 .080 12144014 16 


96 Window Glass in the Making 


Glass that is slightly thicker than the maximum) 
specified for that strength is always accepted ; r 


within the specification, unless it is so much thicket 
that it is not suitable for the purpose for which it 


is to be used. A purchaser, however, is not obliged 


to accept glass that is appreciably thinner than the 
minimum allowed for that strength. q| 

As arule, the thickness is judged by the thickness 
of all the glass in the box, and should not be re 


a) 
bee 
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ay 
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and should not be demanded. 


“Tolerances in Thickness in Individual Sheets” 


‘Thickness of individual sheets shall not vary mote 


thickness may be equal to the tolerance allowed for that 


class.’ 
“Sizes Obtainable” (U.S. Govt. Specifications) 


“The maximum dimensions recommended are: 


Width in Length in 
inches inches 


For Single Strength ............ 40 50 4 : 
For Double Strength ........... 60 80 
For Heavy Sheet ...........0.04- (66. 9G 


ee oe. 
Soa aati 3.) , 


Window Glass in the Making 97 


Single strength glass is made up to 54 inches in 
agth, but we do not take orders for sizes in this 
ickness larger than 84 united inches. Nor do we 
ke orders for heavy sheet glass in sizes larger than 


be 


“Glass must be cut to dimensions ordered with an al- 
wable tolerance of ¥32" per 1%" of thickness.” 


Flatness” 

“All clear window glass shall be relatively flat. Slight 
weature, provided it is regular, will be allowed, but the 
naximum deformation or bow shall not make an arc 
sigher than 0.5% of the length of the sheet. Reverse curve 
r crooked glass is not allowable.” 

Since the above was published we have developed 
|new process of flattening, which enables us to pro- 
luce window glass that is absolutely flat from any 
sommercial or practical standpoint. We guarantee 
his new-process-flattened glass to be as flat as any 
window glass made by any other process. 

This new process also anneals the glass better 
han the old process, which makes it softer to cut 
and less liable to break in handling than the glass 
lattened and annealed by the old methods. 


: “GLAZING” 
“Window os should ALWAYS be glazed with the 


convex side out.’ 


98 Window Glass in the Making 


The above Specification was drawn when practi: 
cally all window glass was bowed, but now the 
greater portion of all window glass produced is flat 

The glazing is one of the most important factor 
in the appearance of the glass. All window glass. 
whether bowed or flat, and irrespective of the proc. 
ess by which it is made, has one side that presents 
a better appearance when glazed to the outside. In 
the case of bowed glass, it is the convex side. When! 
so glazed, such glass not only looks better, but it 
will withstand greater wind pressure and concus- 
sion shocks than if glazed with the concave side out 

From the standpoint of putting the glass into th 
sash, flat glass can be glazed with either side out; 
but from the standpoint of the appearance of th 
glass in the sash, it is just as important to gla ze it 
with the proper side out as it is when glazing 
bowed glass. In glazing flat glass, the side on which 
the glass was cut should be glazed to the outside, 
as all glass is usually cut on the best surface. 

To distinguish on which side the glass is cut, ii 
is necessary to examine carefully the edges of tht 
glass. The edge of the surface on which the glass| 
was cut will have a slightly nicked or roughened 
appearance, made by the cutting tool, while 
under part of the edge will show a slightly wavy 
appearance caused by breaking the glass apart. 


Sr eal grin Se 
Cap eh. em 
bien 


Window Glass in the Making 99 


_ If the windows of a house glazed with window 
glass are viewed from the outside, and present a 
smooth, lustrous appearance, and show clear, well 
defined images of objects reflected in them, one 
may be sure they have been glazed with the proper 
side out. But if they present a rough, battered ap- 
pearance, and distort the images of objects reflected 
in them, they have been glazed with the wrong side 
out. Of course, glass that contains humps and de- 
pressions on its surface will not reflect properly, no 
matter which side is glazed to the outside. 

_ Inthe framing of pictures it is also very important 
that the better side of the glass should be framed to 
the outside. Otherwise it will interfere with a 
proper view of the picture, and portions of it will 
appear distorted. 

All window glass, no matter by what process it 
is made, has a ‘‘grain’’ that extends in the direction 
the glass was drawn. Ordinarily, in glazing, this 
“grain” should be vertical in the sash or frame, as 
the glass presents a much better appearance when 
viewed in a reflected light if so glazed. But when 
glazing sash to be used in automobiles, railroad 
coaches, or other vehicles, the “‘grain’’ should be 
horizontal in the sash. When so glazed the view 
from the vehicle is clearer and freer from distortion 
than when the “‘grain’’ is vertical in the sash. When 


i Pe tea 


100 }6© Window _ Glass in the Making 


ordering glass for vehicles, the dimension that is to | 
extend horizontally in the sash should be specified 
first, and the vertical dimension last, in order tha t | 
the glass may be cut accordingly. | 


STRENGTH OF “THE BEST GLASS” 


In order to produce a grade of window glass that | 
would be justly entitled to be called ‘The Best 
Glass,’’ judged from every standpoint, the Ameri= 
can Window Glass Company used the results : a 
very large number of scientific and practical tests of 
numerous kinds of glass. Those tests include th 1c 
following: ; 

Tensile strength; elasticity by bending and tor 
sion; strength of glass in frames to show its resis- 
tance to impact, to slow loading at the center, and 
to uniform loading over the entire area; annealing; 
extent of expansion by heat; determination of the 
modulus of rupture by bending, impact, loading. 
and torsion; chemical composition; and others. — 

Many of these tests were made by the Unite 
States Bureau of Standards which tested approx 
imately 5000 samples of glazing glass of various 
types and makes for strength with transverse loam 
and impact to determine the modulus of ruptur 
Several thousand samples were also tested for var- 
ious properties in the laboratories of the University 
of Pittsburgh and other testing laboratories. 


Window Glass in the Making ror 


MODULUS OF RUPTURE 


Of all the tests made, that of the modulus of rup- 
ture is the most important to the glass user. The 
technical term ‘‘modulus of rupture’’ is ‘‘the meas- 
ure of the force which must be applied in order to 
produce rupture,’’ z.e., to break the glass, when 
subjected to tests for bending, impact, loading, or 
torsion. Its value is expressed in pounds per square 
inch and signifies the average load required to pro- 
duce the rupture under any of the four tests above 
mentioned. 

RESULTS 


Those tests demonstrated the superiority of the 
American Window Glass Company’s brand ‘‘The 
Best Glass” in the matter of tensile strength and 
modulus of rupture over any other window glass, 
plate glass, or rolled glass. 

_ Furthermore its higher modulus of rupture proves 
that ‘“The Best Glass’ will withstand greater wind 
pressure than any other glass. 

For the benefit of those who desire precise infor- 
mation as to the modulus of rupture of our glass, we 
submit a copy of a diagram (Fig. 1) prepared by 
the *United States Bureau of Standards, Department 


of Commerce, showing the modulus of rupture of 
*Presented by A. E. Williams, of the Bureau of Standards, be- 
fore the Glass Division, American Ceramic Society, Pittsburgh 


Meeting, February, 1923. By permission of the Director of the 
Bureau of Standards, Department of Commerce. 


eur, '* 


102 Window Glass in the Making 7 


various thicknesses of clear window glass and \% 
inch polished plate. This diagram shows the ove t 
whelming superiority of the clear window glass in 


\ 


the matter of modulus of rupture. . 3 


ep eee ee ee 


MODULUS OF RUPTURE 


{ 15000 OF CLEAR SHEET AND POLISHED PLATE GLAS 
om RY 
vf Ni Lo ” 
YU vnunet ama 
= 13000 £S Se RY ee 
E: sf go Si. g 
- gh B ss? 3 
S 8 Ss tas 
| 11000 SK —_8_*_f§__* HG 
38 & yy 
: Sos... + Sys 3 
Ww Ss e 
a Ss BS = 
3 * ‘ 
faa] 9000 aus : : eo 
Soa NON ee 
5 7000 
as) 
3 
WEIGHT 
FIG. I 


The figures given in the diagram for the modulus - 
of rupture of clear window glass are identical with 
the figures furnished to the American Window Glass 
Company by the Bureau of Standards, showing the 
results of numerous tests conducted by the Bureau 
of Standards on samples of the American Window 
Glass Company’s glass submitted to the Bureau for 


Window Glass in the Making 103 


purposes of tests. The results of the tests by the 
reau of Standards on the American Window Glass 
ompany’s glass for modulus of rupture were con- 
firmed by similar tests made by other testing lab- 
a 
\ The Tensile strength tests of the American Win- 
ow Glass Company’s brand, ‘“The Best Glass,” 
show a tensile strength of 5100 pounds per square 
inch. Similar tests conducted on other kinds of glass 
demonstrated that none of them approeched the 
tensile strength of ‘The Best Glass.” 


Fourteen Reasons 
- FOR YOUR SPECIFICATION OF 
“The BEST Glass” 


1 Our melting furnaces are the largest iat 
the world and produce perfectly melted 7 
glass. ia 


2 Our improved mechanical process of 
drawing and blowing gives our glass 
greater tensile strength and higher mod- 
ulus of rupture than any other window 
glass, plate glass, or rolled glass; con- 
sequently, it offers greater resistance to 
wind pressure. ‘ 


3 Our latest improvements in our blow- 
ing machines enable us to provide ab- 
solutely perfect cylinders, which make 
it possible to secure the best flattening re 
ever obtained. | 


4 Our new method of flattening gives ou 
glass a perfectly smooth surface, andl 
brilliant polish, unequalled byany orhes 
window glass. 


104 


oe : 
oh Rs Ete ee o a Ay) 
r fh NPT aay Ne at pola nas 
- ee eae wee 


5 


6 


Window Glass in the Making 105 


Our glass has less wave than any other 
glass, and consequently, shows less 
distortion. 

Our glass is flat; it contains no reverse 
curves. 


7 Our glass is uniform in thickness. 


8 


9 


Our glass is perfectly annealed and, 
therefore, does not break as easily as 
poorly annealed glass. 

Our glass is washed and thoroughly 
cleaned in an acid bath, which prevents 
discoloration and permits ready detec- 
tion of defects. 

Our glass cuts perfectly on both sides. 
Our glass is graded to the highest 
standard of quality. 

Our grading is the recognized standard 
for the United States, and is higher 
than the foreign standards. 

Our glass does not break in shipment 
on account of the uniformity of flat- 
ness, well made boxes, great care in 


packing and skillful loading. 


14 Our entire process is conducted on 


scientific principles. 


“AA” Quality 55, 87, 88 
_ Acceptance or rejection of 
_ shipments 86 


Acid Bath 48, 49, 51, 57, 63- 
64, 105 


; “Air supply for blowing 39, 41 
“Analyses of glass 17-74 


Annealing 42, 44, 47-49, 77, 
97, 100, 105 


| Bionealin g lehrs 48, 49 


ae Quality 54, 55, 87, 88— 
91, 94 


PAcchitects specifications 18, 83 
_ Arsenic 26 
_ Ash, soda 26 


# Automobiles, glass for 15, 18, 
73, 99 
a particles in glass 94 
e Beginnings of window 

© glass 1 eyes) 
Bending test 100-103 
- Blisters 59, 84, 85, 89, 90, 92, 94 
- Blowin g cylinders, air 


5 supply 39 
5. Blowing window glass 39, 83, 
: > 104 
_ Blow pipe 39 
‘Bosh, ladle 34 
_ Bow in glass 97, 98 
Boxes, Packing 53, 54, 105 


—“B” Quality 55, 70, 87, 90, 
: 91-92, 93, 94 
_ Branding of boxes 53, 54 
_ Breakage caused by knots 61 
Caused by wrinkles 61-62, 85 
Caused in loading 57 
During manufacture 28 


INDEX 


Due to defects 58, 85, 93 
Due to poor annealing 

48, 105 
In handling 97 
In shipment 93, 97, 105 


Brick cost compared with 
glass 16 


Brilliance of polish 50, 72 
Brittleness, of glass 26, 48, 77 


Bubbles 22, 33, 59 
Bureau of standards 81, 100, 
102, 103 
Burn 61, 84, 85, 89, 91, 92, 94 
“C” Quality 55, 87, 92, 93 
Capping of cylinders 42 
Carbon 26, 63 
Carbonate of soda Pe. 
Carload shipments 86 
Cars, loading 57 
Central area of sheet ~ 84, 88, 
89, 90, 91 
Charcoal, ground 26 
Charging the furnace Be! 
Cheerfulness, promoted by 
clear window glass 16,18 
Chemical composition 
affects quality ¥7. 


Chilling, causes cords, lines 60 
Chinese discovered glass 20 
Chipped glass 67, 74-75, 101 


Clay 58 
Clay pots for melting 31 
Cleaning of glass 105 
“Clear sheet glass’’ 101, 102 
“Clear window glass” 16, 83 
Cleating of boxes 53 
Coal, crushed 26 


Cockles 62, 84, 92 
Coke 26 
Color of glass 26 


“Commercial” Quality 70, 94 


“Common window glass’’ 13 
Comparison of glass 76-77 
Complaints 56, 93 
Composition of glass 25-30 
Concave side of glass 98 
Concussion shocks 98 
Convex side of glass 97, 98 
Cords and Lines 60, 84, 85, 
89, 92 

Corrugations in window 
glass 61 
Cost of window glass 16, 19, 


71, 81, 88, 90, 91,:93,.95 
“Cracking open” 42, 43, 45 
Critical range of annealing 

temperature 47, 48 
Crystal sheet glass 67, 72-74, 
87, 94, 95, 101 


Cullet, used in melting 33 
Curves in glass 97 
Cut sizes 94 
Cutting and Sorting 51-52 


Cutting qualities 48, 97, 105 


Cylinders 36, 37, 39, 40, 41, 
42, 43, 65-66, 104 


53 
57, 63 
Decolorizers 26 
Defects 17, 18, 22, 46, 49, 52, 

53, 58-64, 61-62, 65, 70, 76, 

84, 85, 88, 89, 90, 91, 92, 94, 
95, 97, 104-105 

Defects, location of 90, 91 
Defects, number permitted 91, 
92, 94, 95 

Defects, sizes permitted 90, 91, 
92, 94, 95 


Dampness causes fade 


(et a 


Definition of clear window > 


glass 
Deliquescent glass 29 
Deformation ; 97 


Density of glass 26, 29, 74 
Devitrification 28-29, 58 
Dimensions of window 

glass 97, 99, 100 
Dipping and washing 48- 


Discoloration 27, 30, 49, 53, 57, 
63-64, 74, 105 
Discovery of glass 20 
Dirt and moisture cause 
chemical action . 
Distortion of window glass . 
18, 59-60, 92, 93, 99, 105 
Double strength glass 54-56, 
67, 71-72, 81, 87, 92, 94, 95, 
96, 97; i 
Drawing cylinders 36, 37, 7 
Drawing window glass 36, a % 
38, 66, 77, 83, 104 
Drawn process, flat sheet 48 
Durability of window Z 
glass 29, 30, 72; 7m 
Dwellings, glass for 73, $ 92 


Elasticity of glass 12, 10 0 
Elements, glass keeps out 13 
Evenness of thickness 72, 105 
Examination, method of _ 85 
Expansion by heat test 100 
“Factory Run” Quality 87, 94, , 


Faded glass 27, 30, 49, 53, 5% 
63-64, 74, 85 

Federal Specification 
Boards «82 
Fire finished | 


Flat sheet drawn process 48, 
61, 62, 65, 74, 83 


a. 
63 ni 


. Flattening 43-46, 83, 97, 
104-105 

Flattening defects 46, 61-62, 
97, 104-105 


Flattened sheets 45, 46, 62, 
65, 97, 104-105 

“Flattening stone’’ 45, 62 
Flattening temperature 45, 61 
Flaws in glass 88, 89, 90, 92, 
94, 95, 105 

Flux, nitre as a 20-22 
Foreign grading standards 105 
_ Foreign particles 49, 85, 94 
“Fourth Quality” 55, 87, 92, 


93 
Frosted appearance of 


glass 64, 74 
Furnace operation 32, 33, 58, 
59, 60 
Furnaces for flattening 43 
Furnaces for melting 31, 33, 
35, 104 
Fuel for melting 31 
Gas, for melting 31 
Glazing 97, 98 
**Glazing’’ Quality 87, 94 
Glossy surface of glass 83 
Glue coating 74 
Government Specifica- 
tions i gor 
Government tests 48 


Grade measured by 
defects 17-19, 84, 85, 88, 89, 
90, 91,92, 94, 95, 105 
Grades, substitution of 54-56, 
81, 82, 93 
Grading, rules for 81-103 
Grading glass 51, 52, 81-103, 
105 
' Grain in glass 99 
Greenhouses, glass for 15 
Ground glass 67, 74-75, 101 


Hand blown window glass 37, 

42, 68, 83 
Handling of glass 48,62, 71,97 
Health, glass aid to 16, 18 
Heat, Conductor (glass) 12 
Heat test 100 
Heavy sheet window glass 94, 


96, 97 

“Horse”’ for receiving 
cylinders 39, 42 
Hot bed sash 93 
“Hum” 63 
Humidity affects glass 29 


Humps in window glass 62, 99 


Hygroscopic glass 29 
Impact tests 100-103 
Imported glass 68, 70, 73 


Ingredients, proportion of 58 


Inspection 52 
Iridescence on the surface 

of glass 64 
Iron causes greenish tints 26 
Iron, heated for splitting 42 
Kelp glass 22 
Kiln, heat drawing 37, 41 
Kiln, heat drying 74 
Knots 60-61 


Labeling quality and thick- 
ness 54-56, 70, 73, 90, 92 
Ladling and blowing 37-42 
Lantern slides 15, 67, 68-69, 95 
Laws, tariff 13 
Lehrs, annealing 44, 48 
Light, glass lets in 13, 14, 16 
Lights, paper between 70, 73 
Lights per inch 95 
Lights, sizes of 93 


Light transmitted through 
glass 70, 75 


26, 27, 29, 30, 64, 74 
Lime, burnt 26 
Limestone 26 
Lines 60, 84, 85, 89, 90, 92, 94 
Loading 57, 100-103, 105 
Lubbers, John, inventor 37 


Lumber, cost compared 
with glass 


Lustre of glass 


Lime 


16 


19, 44, 45, 64, 
70, 104 


Machine blowing 83, 104 

Machine, drawing and 
blowing 

Manganese 

- Master Specifications 79-97 

Materials used 58, 59 


Mechanically drawn and 
blown cylinders 36 


Melting and refining 31-35, 104 
Melting defects 58-60, 76 


Sipe 
26 


Microscopic slides 15, 67, 
68-69, 95 

Mirrors 15, 70, 73 
Mixing of materials 58, 59 
Modulus of rupture 27, 77, 
100-103, 104 

Moisture, action of 27, 30 


Moisture causes fade 53, 57, 63 
Muriatic acid 48, 51, 57, 63 


Natural gas for melting 31 
Nitre, used in making 
glass 20-235:22 
‘“‘Non-scatterable” glass 69 
“OB” Quality 94 
“Off-Quality” glass 55, 92, 
93, 94 
Opaque glass 64 
Optical glass 48 


Origin of glass 13, 20-23 
Oven, annealing 47, 48 
Ovens, flattening 43, 45, 48, ou 


335 105, 
70, Ba 


Packing 
Paper between lights 
Partitions, glass for 75, 
Photo dry plate glass 15, 67, 
68-69, 95 
Physical properties affect 
quality i 
Physical strength 72 
Physical structure of glass 42 
Picture glass 15, 18, 67, 69-70, 
90 


Pipe, blow | 
15 
15. 


Plates, photographic 
X-ray > 
Plate glass 73, 76, 77, 101, 
102, 104 
Polish, brilliance of 72, 104 
Polisher for flattening 45 
Polished plate glass 101, 102, ; 
04 
Polish produced in flatten- “a a 
ing 44, 45, 104 
Pompeii, glass found in 27 : 
Porcelain of Réaumur 28 
Pots, clay, for melting 318 
Pot, reversible 37, 395 4. 
Pressure, wind 71, 98, 102,104 
Price of window glass 16, 71, 4 
81, 88, 90, 91, 93, 95 
Processed glass 67,74-75, 101 : 


Producer gas, used for 
melting 


Production of American 7am 
dow GlassCo. 15, 104, 105 


Pyrometer couple po 
“oy 


Quality labels RB : 


yt 
aan 


Quality of materials 58, 59 
Quality slips 54, 55, 70, 92 
Quality of window glass 17- 

19, 26, 55, 81-103,105 


Raw materials melted 33 
Ream 59-60, 83, 84, 90, 92 
Refining process 33 
Regenerative tank system 31 
Rejection of shipments 86, 93 
Resistance to impact 100-103 
Reverse curves a. 
Rippled appearance 65 
Rolled glass 76, 77, 102, 104 


Rules for grading 81-103 
Rupture, modulus of 27, 77, 

100-103, 104 
Rust 63-64 
Rye straw for packing 53 
Salt cake 25 
Salt, glass is a 12 
Sandblasting 74 


Sand, imbedded in knots 61 


Sand, used in making 
glass 12, 20-22, 25 


Shipments 48, 57, 86, 93, 97, 
105 
Shocks, concussion 98 
Silica, used in glass 
making 25, 27, 29, 30, 58, 74 
Single strength glass 54-56, 
67, 71-72, 81, 86, 87, 92, 93, 
94, 95, 96, 97, 101 
16-o0z. picture glass 67, 69-70 
Size of cylinders 41 
Size of defects permitted 90, 
91, 92, 94, 95 


Sizes, cut 94 
Sizes obtainable 96 
Sizes of lights 93 
Sizes of sheets 51,52 


Slides, lantern 15, 67, 68-69, 95 


Slides, microscopic 15, Gi, 
68-69, 95 

Smooth surface of glass 70, 83, 
104 

Soda ash 26 
Soda used in making glass 21, 


22, 25, 26, 27, 29, 30, 64, 74 
Sorting 52 
Specifications, Government 


Scratches 62-63, 84, 85, 89,94| Complete 79-97 
Screens, glass for 75| Clear window glass 86-87 
Seaweed, furnishes kelp 22 | Stain . 30, 63-64, 74, 85 
Seeds and blisters 58-59, 84,| Standards, Bureau of 81, 100, 
| 85, 89, 90, 91 102, 103 
Segments of cylinders 42, a Standards for grading 105 
5 : 
S , flattenin 45, 62 
““Selected’’ Quality 70 Pee metas 58, 84, 85, 94 
Selected stock sheets 95 seapet . ee gee 
Sheet drawn window glass 37, Bree eats mV etChonncs 31, 
48, 61, 62, 65, 74, 83; ee bi 
Gicer celected stock g5 | Storing raw materials in 
Dh, bins 24 
Sheets, sizes 51, 32 f ki 
Shipment, breakage in 93, 97, pO Dees. = 
105 | Streaks 59, 83 


Strength, single and double 
54-56, 67, 71-72, 81, 86, 87, 
92, 93, 94, 95, 96, 97, 101 
Strength of window glass 12, 
27,29, 303-42, TL, 73; 7 4e0 Ws 
100-103, 104 
Stretching strains 66 
Strings 60, 84, 89, 90, 94 

Substitution of grades and 


qualities 54-56, 81, 82, 93 
Sulphate of soda 25, 26 
Sunlight, glass letsin 13, 14, 

16 
Superfine “Quality” 70 


Surface, brilliance 
' Sweating of glass 


30, 72 
29, 49, 63 


Tanks for melting 31 


Tariff laws, window 
glass in 13 


Temperature changes 65-66 
Temperature, flattening 45, 61 
Temperature, melting 33, 35 
Temperature, annealing 47, 48 


Tensile strength of glass 12, 
42, Fis 73; 74, 4 iy 100-103 


Terms of clear window 


glass 84 
Testing glass 17, 38, 48, 100- 
103 

‘The BEST Glass” 19, 72, 


77, 82, 100, 102, 103 
Thickness of picture glass 70 


Thickness of window 
glass 55, 67, 73, 81-97, 101, 
102, 105 


34-oz. crystal sheet 67, 71-T4e : 
87, 94, 95, 101 4 

39-oz. crystal sheet 67, 72-7an 
87, 94, 95, 101 

Tile, cost compared with ae 
glass 16 . 
Tolerances in thickness 95,96 
Torsion test 100-103 
Toughness of window a 
glass 6, 42 
Transmission of light ee 
through glass 70, Toa 
26-oz. glass 67, 72, 87, 94, 95, _ 
101 y 

29-oz. glass 67, 72, 87, 94, oa 
ap 


eS 
4 
at 


42, 
103 xs 
United States Bureau of oS 
Standards 81, 100, 102, 103 S 
Bris 


United States Government 
Master Specifications 79-97 ci 


United States grading a . 
standards a = 


Te 


Uniformity of thickness 


Warehousing and shipping ay) 
Washing of glass 105 , 
Wave in window glass 59-60, — 
65-66, 83, 85, 89, 90, 91, 105 — 
Weights of window glass 67, 95 
Wind resistance 71, 98, 102, a 
104 

73,99 

35, 599 

61-62, 85, 94 


Windshield glass 
Working zone 
Wrinkles 


X-ray glass 4s, 67, 68-69, 2 


